Technical Fisheries Committee Administrative Report 2003:

Technical Fisheries Committee Administrative Report 2003:
Status of Lake Trout and Lake Whitefish Populations in the
1836 Treaty-Ceded Waters of Lakes Superior, Huron and
Michigan in 2002, with recommended yield and effort levels for
2003
A Report Submitted by the
Modeling Subcommittee
to the
Technical Fisheries Review Committee
A.P. Woldt (United States Fish and Wildlife Service),
S.P. Sitar (Michigan Department of Natural Resources),
J.R. Bence (Michigan State University),
and M.P. Ebener (Chippewa/Ottawa Resource Authority),
Editors
December 2004
Recommended Citation formats.
Entire report: Modeling Subcommittee, Technical Fisheries Committee. 2004. Technical
Fisheries Committee Administrative Report 2003: Status of Lake Trout and Lake
Whitefish Populations in the 1836 Treaty-Ceded Waters of Lakes Superior, Huron and
Michigan in 2002, with recommended yield and effort levels for 2003.
http://www.michigan.gov/documents/dnr/2003-status-report_198235_7.pdf
Section: Woldt, A.P., Bence, J.R., and Ebener, M.P. 2004. Executive Summary in
Woldt, A.P., Sitar, S.P., Bence, J.R., and Ebener, M.P. (eds.). Technical Fisheries
Committee Administrative Report 2003: Status of Lake Trout and Lake Whitefish
Populations in the 1836 Treaty-Ceded Waters of Lakes Superior, Huron and Michigan in
2002, with recommended yield and effort levels for 2003.
http://www.michigan.gov/documents/dnr/2003-status-report_198235_7.pdf
2
Table of Contents
Executive Summary ............................................................................................................ 4
Stock Assessment Models................................................................................................... 8
Recommendations and Future Directions to Improve Assessments ................................. 18
Status of Lake Trout Populations ...................................................................................... 24
Lake Superior ................................................................................................................ 24
MI-5 (Marquette - Big Bay) ..................................................................................... 24
MI-6 (Au Train - Munising)..................................................................................... 27
MI-7 (Grand Marais)................................................................................................ 30
Lake Huron.................................................................................................................... 33
MH-1 (Northern Lake Huron).................................................................................. 33
MH-2 (North-central Lake Huron)........................................................................... 38
Lake Michigan............................................................................................................... 43
MM-123 (Northern Lake Michigan) ........................................................................ 43
MM-4 (Grand Traverse Bay) ................................................................................... 47
MM-5 (Leelanau Peninsula to Arcadia)................................................................... 51
MM-67 (Manistee - Ludington) ............................................................................... 55
Status of Lake Whitefish Populations ............................................................................... 59
Lake Superior ................................................................................................................ 59
WFS-04 (Marquette - Big Bay)................................................................................ 59
WFS-05 (Munising) ................................................................................................. 62
WFS-06 (Grand Marais)........................................................................................... 65
WFS-07 (Tahquamenon Bay) .................................................................................. 68
WFS-08 (Brimley).................................................................................................... 72
Lake Huron.................................................................................................................... 76
WFH-01 (St. Ignace) ................................................................................................ 76
WFH-02 (Detour)..................................................................................................... 80
WFH-03 (Drummond Island)................................................................................... 84
WFH-04 (Hammond Bay)........................................................................................ 86
WFH-05 (Alpena) .................................................................................................... 90
Lake Michigan............................................................................................................... 93
WFM-01 (Bays de Noc)........................................................................................... 93
WFM-02 (Manistique) ............................................................................................. 97
WFM-03 (Naubinway)........................................................................................... 101
WFM-04 (Beaver Island) ....................................................................................... 105
WFM-05 (Grand Traverse Bay)............................................................................. 109
WFM-06 (Leland - Frankfort)................................................................................ 114
WFM-07 (Ludington)............................................................................................. 117
WFM-08 (Muskegon) ............................................................................................ 120
Appendix 1. Lake whitefish management units. ............................................................ 123
Appendix 2. Lake trout management units. ................................................................... 124
3
EXECUTIVE SUMMARY
Prepared by Aaron P. Woldt, James R. Bence, and Mark P. Ebener
models resulted in estimates of
abundance and mortality which were
combined with growth and maturity data
for whitefish and lake trout in each stock
or management unit to project
recommended yield levels (upper
bounds) for calendar year 2003.
Recommended yield limits were
obtained by either limiting mortality to a
maximum rate, achieving a minimum
spawning potential reduction, or
projecting harvest for a specified level of
fishing effort. The maximum allowable
mortality rate (A) on whitefish was 65%,
while the maximum mortality rate on
lake trout was either 40 or 45%. In some
areas the mortality rate was not
considered for lake trout, and yields
were instead tied to levels of fishing
effort as part of a process for "phasing
in" total mortality rate targets as
specified in the Consent Decree. The
target spawning potential reduction for
whitefish ranged from 20 to 35%.
Harvest limits were allocated to State
and CORA fisheries for each stock
following the percentages specified in
the Consent Decree.
The MSC’s
recommended harvest and effort limits
for whitefish and lake trout are provided
in the table below. The actual harvest
limits that were imposed, based on terms
of the Consent Decree, or harvest
regulation guidelines (HRGs) are
detailed later in the text and summary
table for each management unit.
Asterisks in the table below depict units
where the recommended yield limit
differed from the actual yield limit.
In August 2000 the State of
Michigan’s Department of Natural
Resources (MDNR), five tribes of the
Chippewa/Ottawa Resource Authority
(CORA), and United States Department
of Interior’s U.S. Fish and Wildlife
Service negotiated an agreement
(Consent Decree) to resolve issues of
allocation, management, and regulation
of fishing in 1836 Treaty waters of lakes
Superior, Michigan, and Huron (U.S. v.
Michigan 2000). The Consent Decree
states that mortality of lake trout shall be
regulated with yield and effort limits in
1836 Treaty-ceded waters.
In
management units where the state and
tribes both have commercial whitefish
fisheries, the mortality of whitefish shall
be regulated with yield limits. The
Consent Decree provides specific
guidelines on how these yield and effort
limits should be calculated. A Modeling
Subcommittee (MSC) of the Technical
Fisheries Committee (TFC) was
established and charged with developing
the yield and effort limits required in the
Consent Decree.
The MSC assessed population status
and mortality rates of 16 different stocks
of lake whitefish and ten stocks of lake
trout that are within 1836 Treaty-ceded
waters. Where feasible we developed
and fit statistical catch at age (SCAA)
models using a nonlinear modeling and
statistics program (AD Model Builder,
Otter Research Ltd.) to estimate age- and
year-specific population abundance and
mortality rates. In some cases the
available data did not allow us to
develop reliable population estimates in
this way, and instead we have used a
more descriptive approach.
SCAA
4
Species
Lake trout
Lake
Superior
Michigan
Huron
Lake
whitefish
Superior
Michigan
Huron
Management
unit
MI-5
MI-6
MI-7
MM-1,2,3
MM-4
MM-5
MM-6,7
MH-1
MH-2
Yield limit
(lb)
119,100
50,700
*88,300
*287,700
*80,000
107,800
471,700
163,000
82,100
Gill-net limit
(ft)
NA
2.98 million
4.05 million
9.36 million
1.03 million
0.57 million
NA
8.67 million
NA
WFS-04
WFS-05
WFS-06
WFS-07
WFS-08
WFM-01
WFM-02
WFM-03
WFM-04
WFM-05
WFM-06
WFM-07
WFM-08
WFH-01
WFH-02
WFH-03
WFH-04
WFH-05
200,000
745,000
98,000
502,000
*67,000
1,018,000
514,000
1,462,000
540,000
345,000
221,000
no estimate
1,852,000
375,000
*221,000
no estimate
*333,000
875,000
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
the recreational fishery.
Work
continues on the MI-6 model to verify
its performance and stability. In MI-5
and MI-7 recent mortality rates have
been below targets, and increases in
yield are possible. There have been no
efforts to fit a stock assessment model
for lake trout in MI-8 of Lake Superior
because this is a deferred area. There
has been a general decline in size-at-age
of lake trout across Lake Superior over
the past 20 years, and tied to this is a
shift toward later maturity. These
changes in growth and maturation
In Lake Superior there are selfsustaining stocks of lean lake trout, and
the SCAA models and target mortality
rates apply to these wild fish in three
management areas (MI-5, MI-6, and MI7). In MI-6 and MI-7 siscowet and lean
yield are combined in commercial catch
reports, thus allowable total yield (leans
and siscowets) can exceed the values in
the above table by 13% and 41%
respectively. In MI-6 recent mortality
rates have been below the target, but
recreational harvest exceeded the harvest
limit (2002) despite strict regulation of
5
below recent observed yields in this
area. Decreases in commercial fishing
effort and increases in the minimum
size limit for the recreational fishery
should help to achieve mortality targets.
In MM-5, mortality rates have been less
than the target rate. Lamprey mortality
is not declining in Northern Lake
Michigan. Lake Michigan researchers
suspect that another stream(s) like the
Manistique River may be producing
large numbers of sea lamprey in
northern Lake Michigan. It is hoped
that future treatment of the Manistique
River will lead to reduced levels of sea
lamprey induced mortality in northern
Lake Michigan.
In general, fishery exploitation in
recent years has not been excessive on
lake whitefish stocks. However, size at
age has declined for most stocks over
the past two decades. In a number of
stocks this has been accompanied by a
decline in fish condition (weight for a
given length). These patterns are seen
for some stocks in Lake Superior, but
are most evident in Lake Michigan and
Lake Huron management areas. Many
stocks experienced a decline in
recruitment near the end of the time
series used in the assessments. Again
this pattern was most prevalent in Lake
Michigan and Lake Huron. In WFS-08,
WFH-02, WFH-03, and WFH-04
harvest regulation guidelines were set
based on recent yield levels. If harvest
is maintained at recent levels in the face
of declining recruitment and growth,
mortality rates will be excessive and
will decrease population abundance and
further reduce yield.
In addition,
widespread declines in growth rates of
lake whitefish are a concern, and further
research on this is important for
supporting management strategies. A
summary report is included for WFM-
probably reflect increases in predator
fish abundance and declines in the
abundance of prey fish, most of which
are less abundant than 20 years ago.
Competitive effects of siscowet lake
trout may also play a role.
In the Lake Huron and Lake
Michigan management areas, wild lake
trout are scarce and the assessment
models and target mortality rates apply
to stocked fish. In MH-1 lake trout
mortality rates are above target rates but
have been declining, while in MH-2
mortality rates are below target rates.
Phased-in reductions in fishing mortality
resulting from reduced commercial
effort and a more restrictive minimum
size limit (slot) in the recreational
fishery should continue to improve the
situation in MH-1. The recent decline in
sea lamprey mortality in MH-2 is the
main reason that total mortality is below
target in this area. Continued decline of
sea lamprey mortality in MH-1 and MH2 is probably necessary to reach or
maintain
mortality
rate
targets.
Indicators for Lake Huron show
substantial decreases in sea lampreyinduced mortality due to treatment of the
St. Marys River. Future success in
controlling sea lamprey may allow
increases in lake trout yield in Lake
Huron.
In Lake Michigan lake trout
mortality rates are well below target
rates in the southern most area.
Northern Lake Michigan unit MM-123
lake trout mortality rates have been near
target rates.
However, estimated
declines in abundance and the Consent
Decree’s requirement for phased-in yield
limits result in potentially higher
mortality rates in the near term. In MM4, mortality rates have been higher than
the target rate. As a result, the 2003
recommended yield limit for MM-4 is
6
in this report occasionally deviates from
the true harvest. This is due to the cutoff date for data inclusion in models
that requires the MSC to occasionally
use preliminary harvest numbers. The
proposed procedures for handling yield
and age composition data are aimed at
ensuring adequate time after the data
are available for analysis, modeling, and
diagnostics. We also believe that the
parties should consider revisions to the
time line for preparing stock
assessments. First, we believe it would
be more efficient if the whitefish stock
assessment models and the lake trout
models followed the same time
schedule. Second, we think there needs
to be more time between when the MSC
obtains data from the parties, provides
initial yield and effort limits to the TFC,
and when the TFC provides those
numbers to the parties. This would
allow the MSC time to review
procedures for problematic estimates,
conduct adequate model diagnostic
analyses, and to explore different
options suggested by the TFC.
07, but modeling efforts to describe this
stock currently have little utility for
estimating allowable harvest due to lack
of data. This area was not fished
commercially between 1985 and 2000.
Since 2001, there has been a small
amount of tribal commercial harvest in
WFM-07 by the Little River Band of
Ottawa Indians.
In addition to providing assessments
for each stock, we also provide
recommendations to the TFC to improve
data collection and to improve the
SCAA models. These recommendations
include developing fishery-independent
surveys to assess abundance of lake
whitefish, delineating stock boundaries
and movement patterns, determining
under-reporting and discarding rates,
improving natural mortality estimates,
refining estimates of hooking mortality
on lake trout and incorporating hooking
mortality into all lake trout models,
improving the estimation of selectivity
curves, refining our methods of
estimating lake trout recruitment, and
developing methods of estimating timevarying
catchability.
The
implementation
of
all
these
recommendations will take several years
and will involve a significant and
increased investment in staff, time, and
other resources.
We also recommend a process that
will allow us to provide timely stock
assessment results.
In part this is
targeted at meeting deadlines imposed
by the Consent Decree. This process
involves using the projected yield for the
last few months of the year based on
historic patterns of the yield, modifying
the commercial yield compilation
process, and forgoing the most recent
year's age composition data when it
cannot be available by the deadline. We
duly note that annual harvest referred to
7
STOCK ASSESSMENT MODELS
Prepared by Shawn P. Sitar and James R. Bence
Overview
We used age-structured population
models in two ways. The first was as a
means to generate estimates of lake trout
and lake whitefish abundance and
mortality rates and describe how these
have changed over time. The second
was to project yield, harvest amounts,
and associated effort that met criteria
established as part of the 2000 Consent
Decree. The first of these tasks was
accomplished
through
applying
statistical catch-at-age analysis (SCAA)
as a means of estimating parameters
determining fish abundance and
mortality.
These catch-age models
operated with annual time steps and agespecific abundances. Mortality rates
were estimated for each year through the
last year for which data were available.
Models were developed for stocks in
each defined management area.
The second task built from the first,
by projecting the estimated fish
population forward through the 2003
fishing season, accounting for expected
fishing and natural mortality and
projecting the associated harvest and
yield. The fishing mortality rates were
adjusted in these projections to match
upper bounds on fishing effort, fishery
harvest, or total mortality while
satisfying state and tribal allocation as
defined in the Consent Decree.
a submodel that predicted observed data,
given the estimated population each
year. The agreement between the model
predictions and observed data was
measured by statistical likelihood. Both
the
population
and
observation
submodels
included
adjustable
parameters. Any given set of these
parameters corresponded to a specific
sequence of stock abundances, mortality
rates, and predicted data. The set of
such parameters and associated stock
dynamics and mortality rates that
maximized the likelihood (the maximum
likelihood estimates) was taken as the
best estimate.
Statistical Catch-Age Analysis
A catch-age model was fit to
available data. Each model consisted of
two components.
The first was a
submodel that described the population
dynamics of the stock. The second was
where Za,y was the instantaneous
mortality rate for age-a and year-y.
Total annual mortality (A=1-P) increases
with increasing Z, but asymptotes at 1.0.
Mortality targets were usually expressed
Population submodel
The basic population model was
quite simple. Except for the first age
and first year, abundance-at-age at the
start of each year was calculated
recursively as the proportion of the
cohort surviving from the start of the
previous year:
N a +1, y +1 = N a , y Pa , y
The proportion surviving was modeled
as
Pa , y = e
8
− Za, y
shaped relationship between selectivity
and age, and includes asymptotic
increases with age as a special case.
When time-varying selectivity was
desired, one of the parameters of this
function (that controls selectivity for
younger ages) was allowed to vary
gradually over time, following a
quadratic function in time.
Thus,
selectivity patterns over time were
described by the three parameters of the
quadratic function and the three other
parameters of the logistic function.
Fishing intensity was the fishing
mortality rate for ages that had a
selectivity of 1.0. Fishing intensities
were not estimated freely, but instead
were assumed to be proportional to
effort, up to a multiplicative deviation:
in terms of A, but could be expressed in
terms of the equivalent Z.
A primary challenge in developing
the stock assessment models was to
break the total instantaneous mortality
rate into components of interest that can
be calculated from a suite of parameters,
which can be estimated from available
data. All the models include fishing
mortality (F) and background natural
mortality (M). All lake trout models and
whitefish models for Lake Huron
include sea lamprey induced mortality
(ML). In addition, fishing mortality was
usually broken into two subcomponents.
Thus:
Za, y = F (1) a , y + F (2) a , y + M a + MLa , y
where F(1) and F(2) represent two
fishery components (e.g., gill nets and
trap nets, or sport and commercial). It
was not possible to estimate all these
rates as independent age- and yearspecific components. To reduce the
number of parameters, for each fishery
component, the age- and year-specific
fishing mortality rates are products of
age-specific "selectivity" and yearspecific "fishing intensity". In a purely
separable model, selectivity was
constant and thus each fishing mortality
component was the product of an age (S)
and year (f) effect:
f (i ) = q (i ) E (i ) y ζ (i ) y
where q was catchability (the
proportionality constant), E was
observed effort, and ζ was the deviation.
During model fitting, large estimated
deviations were penalized. However, in
cases where fishery effort was not
considered to be very informative
regarding fishing mortality (generally for
the lake trout models), this penalty was
reduced to near zero making the
procedure nearly identical to estimating
the f(i) directly.
The background natural mortality
was assumed to be constant over time.
For lake whitefish models and models of
wild lake trout in Lake Superior, M was
assumed constant for all ages modeled,
whereas for other lake trout models, M
was allowed to be higher for the younger
ages. For the whitefish models M was
assumed known based on a published
relationship between M and growth
model parameters and water temperature
(Pauly 1980). For lake trout, while M
F (i )a, y = S (i ) a f (i ) y
In many of our assessment models
we have relaxed the separability
assumption, to account for changing
selectivity resulting from changes in
size-at-age, fishery behavior, or other
causes. To do this we modeled the
relationship between selectivity and age
with a four-parameter double logistic
function that provides a flexible dome9
sea lamprey mortality of whitefish was
collected during late summer and fall
(Spangler et al. 1980). Age-specific
marking rates for whitefish were
estimated from year-specific marking
rates and a long-term average marking
rate in each management unit as:
was estimated during model fitting,
deviations from prior estimates, based on
the same relationship used for whitefish,
were penalized.
Sea lamprey mortality rates were not
estimated during model fitting. Instead
they were calculated based on observed
wounding (sum of A1-A3 marks), as
was done by Sitar et al. (1999). For a
given size of lake trout, sea lamprey
mortality was calculated by:
ML = w
m a ,t =
(1 − p )
p
ma , y
 mt − m y
1 − 
 mt



where m is the average number of sea
lamprey marks per fish, a is age class, t
is year, and y is the time series under
consideration. The time series varied
somewhat by management unit but
typically covered 1980-2001 in Lake
Huron units. Essentially, the average
marking rate on an age class was a
function of the annual deviation in sea
lamprey marking in a management from
the long-term average marking rate in
that unit and the average long-term
marking rate on each age class. Sea
lamprey-induced mortality was then
calculated as in past years (Bence 2002)
given a probability of survival of 0.25
from a sea lamprey attack.
In summary, 4 to 6 parameters were
estimated during the fitting of the SCAA
models to describe each fishery's
selectivity pattern, and a year-specific
parameter was estimated associated with
each fishery’s fishing intensity. We
estimated
from
zero
parameters
(whitefish) up to two parameters
(stocked lake trout) to describe
background natural mortality.
No
additional parameters were estimated
during model fitting to describe sea
lamprey mortality, as these rates were
calculated directly from wounding data.
In order to complete the population
model and describe stock dynamics over
where w was the mean wounds per fish
and p was an estimate of the probability
of surviving an attack. Length-specific
wounding rates were converted to agespecific rates using an age-length key.
Lake Huron sea lamprey-induced
mortality on lake whitefish
In past stock assessments for Lake
Huron lake whitefish, sea lampreyinduced mortality was calculated for
specific length classes of whitefish in the
spring, then an age-length distribution
was applied to the length-specific
mortality rates to estimate age-specific
sea lamprey mortality of whitefish
(Bence 2002).
These age-specific
mortality rates were assumed to be
constant across years and constant across
management units and input as data to
the stock assessments in Lake Huron as
a matrix of age- and year-specific sea
lamprey mortality rates.
The method for calculating sea
lamprey-induced mortality of whitefish
in Lake Huron changed in the 2003
stock assessments. Marking rate data
collected during August through
December was used to estimate sea
lamprey
mortality,
because
the
probability of survival used to estimate
10
time it was necessary to specify the
initial numbers at age in the first year
and the recruitment of the youngest age
in each subsequent year. In the simplest
cases each of these would be estimated
as a free parameter during model fitting.
We deviated from this simplest case in
various ways. For stocked lake trout
stocks, we modeled recruitment as the
number of yearling equivalents actually
stocked and calculated to move into an
area
(see
Movement
Matrices)
multiplied by a year-specific "survival
adjustment" factor. In this case the
"survival adjustment" factors were
estimated as parameters, with values
deviating from 1.0 being penalized.
Wild lake trout recruitment was modeled
as a random walk function which was
the product of the prior year’s
recruitment and a multiplicative
deviation.
The recruitment in the
starting year of the model was estimated
as a formal model parameter. Lake
whitefish recruitment was estimated for
each year, with deviations from
recruitment expected based on a Ricker
stock-recruit function (with parameters
estimated during model fitting) being
penalized. For stocked lake trout stocks,
when age composition data was limited
in earlier years, initial age compositions
were based on the known number of lake
trout that were stocked and a rough
estimate of annual mortality, rather than
being estimated during model fitting.
For all the hatchery lake trout stocks,
initial numbers for year classes known
not to be stocked were set to zero.
yearling lake trout stocked into a
management unit was calculated as
follows. First, we assumed that lake
trout recruitment was based on stocked
yearlings or fall fingerlings.
The
numbers of yearling equivalents were
calculated as the number of yearlings
stocked that year plus 0.40 times the
number of fall fingerlings stocked the
year before. Next the numbers stocked
at various locations were adjusted for
movement soon after stocking (before
substantial spatially-varying mortality
comes into play). This was done by
apportioning fixed proportions of the
numbers stocked at each location as
being effectively stocked into each of the
management areas (recruitment location)
on the lake.
These translations of
numbers from stocking location to
recruitment location were in the form of
a "movement matrix."
The numbers
effectively stocked to a management unit
(recruitment location) were then
summed over the stocking locations.
These effective numbers stocked were
the input that was then adjusted upward
or downward to account for yearspecific variations (see above).
The observation submodel
The observation submodel predicts
numbers of lake trout or lake whitefish
killed by each fishing component by age.
For the lake trout models survey catch
per unit effort (CPUE) by age is also
provided.
Fishery kill was then
converted into proportions-at-age and
total number killed for comparison with
data. Likewise, age-specific CPUE was
converted into proportions-at-age and
total CPUE for comparison with
observed data.
Fishery kill was predicted using
Baranov's catch equation:
Movement Matrices and the calculation
of yearling equivalents stocked
Assessment models for lake trout on
lakes Michigan and Huron were for
hatchery-reared lake trout stocked into
the lakes. The effective number of
11
C (i )a, y =
F (i ) a , y
Z a, y
under the assumption that total fishery
kill and effort deviations were lognormal
and that the proportions-at-age were
determined
by
a
multinomial
distribution.
When a survey was
available, this provided two likelihood
components: one for the total CPUE
(lognormal) and one for the age
composition
(multinomial).
An
additional component came from
variation about stock-recruit functions or
numbers based on stocking. In the
calculation of this penalty term, the
deviations were treated as lognormal.
When variation about a prior estimate of
M was allowed, this contributed another
term to the likelihood, and these
variations were also assumed to be
lognormal.
These various components were
weighted by either the inverse of the
variance
associated
with
them
(lognormal components) or the effective
sample size (multinomial components).
Here if X was lognormally distributed,
variance refers to the variance of ln(X).
In the case of effort deviations, in those
cases where effort was assumed to
provide little information on fishing
mortality these components were downweighted by an arbitrarily small value.
The square root of the log-scale
variances for the lognormal variables
was approximately equal to the
coefficient of variation (CV) on the
arithmetic scale. In the case of a
multinomial variable:
N ay A(i ) ay
Note that no additional parameters not
already needed for the population
submodel needed to be estimated.
Survey CPUE was predicted
assuming
proportionality
between
population abundance and expected
CPUE, with selectivity following a
logistic or double logistic function of
age:
CPUE a , y = q ( s) S ( s ) a N a , y
where q(s) was survey catchability, and
S(s) was survey selectivity. In some
cases survey selectivity was allowed to
vary over time in the same way as was
fishery selectivity. The parameters of the
survey selectivity function and survey
catchability were new parameters that
needed to be estimated which were not
needed for the population submodel.
The Likelihood (defining the best fit)
For numerical and coding reasons it
was convenient to maximize the
likelihood by minimizing the negative
log likelihood. Let L stand for the total
log-likelihood. This was calculated as
the sum of a set of K independent
components:
L = L1 + L2 + L3 + … + LK
Each component represents a data source
or penalty, and the number of
components varied among stocks and
species. For each fishery that was
included in the model there were three
components: one for the total fishery kill
each year, one for the fishery age
composition each year, and one for the
effort deviations for each year. These
likelihood components were calculated
CV ( p) =
p(1 − p )
N
With these relationships in mind the
modeling group considered information
on the likely measurement error
associated with the various data sources
and specified default variances for each
12
We then describe how the procedures
were modified to account for specific
details that only apply to some areas.
For some areas these details include how
the target mortality rates were "phasedin" as documented in the Consent
Decree.
type of data, which were adjusted in
cases where additional information was
available on data quality.
In the case of variations about
recruitment expected based on either the
stock-recruit function or the numbers
stocked, an iterative approach was
followed during model fitting. An initial
value for the standard deviation for
variations about expected values was
specified and the model was fit. Then
the standard deviation of the resulting
deviations was calculated. The model
was refit, adjusting the value of the input
standard deviation until the deviation
between the standard deviation value
specified prior to model fitting and the
value calculated after model fitting was
minimized. A minimum deviation was
defined when the ratio of pre- to poststandard deviation was closest to 1.0.
Target Mortality Rates
The Consent Decree specifies a
"fully-phased in" upper bound target for
total mortality (i.e., A = the proportion
of the population that dies in a year).
These rates were either 40-45%
(depending on area) for lake trout or
65% for lake whitefish.
As
demonstrated by the Interagency
Modeling Group (IMG) during the
period that the Consent Decree was
negotiated, these target rates require
additional structure in order to be
uniquely defined. This occurs because
mortality rates vary among ages, so
whether or not a population was above a
mortality target depends upon what ages
were considered and how the mortality
rates for the different ages were
combined.
Following the procedure of the IMG,
we uniquely define mortality rates by
making use of the idea of spawning
stock biomass per recruit (SSBR). For
lake trout, we first calculate spawning
stock biomass for a default target
mortality schedule. Any age-specific
mortality schedule that produces as
much spawning stock biomass as the
default schedule was considered to be at
or below the target mortality rate. The
default schedule was to have only
natural mortality (excluding sea
lamprey-induced mortality) for ages
below a specified age, and mortality
equal to the target rate for ages equal to
or above the specified age.
The
specified age at which the target rate
Calculation of Recommended Harvest
Regulation Guidelines, Total
Allowable Catch (TAC), and Total
Allowable Effort (TAE)
In
general,
upper
bound
recommendations on yield and effort
were calculated by first estimating
population abundance-at-age at the start
of the year and then adjusting fishing
mortality either to meet mortality targets
or to follow guidelines established in the
Consent Decree for phasing in the
targets. The resulting projection of yield
or the effort associated with the fishing
mortality then formed the basis of the
recommendations.
We start by describing how we
determined the maximum amount of
yield that could be taken, consistent with
a specific upper bound on total
mortality. This was the procedure that
underlies
the
modeling
group's
recommendations regarding harvest
regulation guidelines, TACs, and TAEs.
13
Recruitment was set at a value reflecting
recent levels of recruitment (Lake
Superior) or expected stocking. Note
that assumed recruitment has little
influence on calculations of harvest
during the next year, as these fish are
either not selected or only weakly
selected by the fishery.
Lake whitefish SCAA stock
assessment models were similar to lake
trout models except that the estimates
were based on data two years behind the
year for which a harvest limit was being
calculated. Thus for lake whitefish there
was one additional step, which was
projecting the population for two years.
For
this
projection,
age-specific
mortality rates by source (i.e., trap-net
and gill-net fishing mortality, sea
lamprey-induced
mortality,
natural
mortality) were set equal to rates
averaged over the last three years for
which
estimates
were
made.
Recruitment of lake whitefish for the
two projection years was set to the
average recruitment during the last 10
years for which SCAA estimates were
available.
first applied varied among areas
depending upon maturity schedules and
precedent.
For whitefish a somewhat different
procedure was used to ensure both that
an adequate amount of spawning stock
was achieved per recruit and that more
than one age was contributing
substantially to the spawning population.
This was done following a two-stage
approach. First, overall fishing mortality
rates were adjusted so that during the
projection period total annual mortality
on the age experiencing the highest
projected fishing mortality rate was
equal to 65%. Then the spawning stock
biomass per recruit was calculated for
that scenario.
Spawning potential
reduction (SPR) was calculated by
dividing this by the spawning stock
biomass per recruit, calculated assuming
only background natural mortality. If
SPR was less than 0.2, fishing mortality
was decreased until SPR was equal to
0.2. The approach was developed by
examining various different "rules" and
ascertaining that this approach generally
ensured more than one age class was
contributing substantially to spawning.
A SPR of 0.2 was aggressive by
standards applied in other fisheries and
reflects a perception that lake whitefish
was generally robust to fairly high
fishing rates.
Projections during the 2003 Fishing
Season
Starting with the estimates or
projections of age-specific abundance at
the start of 2003, the population was
projected forward over the year
accounting for age-specific mortality
rates by source, using the same
equations described above for the SCAA
models. Numbers harvested-at-age were
calculated by application of the Baranov
catch equation.
Harvest-at-age was
converted to yield by multiplying
numbers harvested-at-age by weight-atage for the fishery and summing over
ages.
Population at the Start of the 2003
Fishing Year
The SCAA stock assessment models
for lake trout directly estimate
population abundance at the start of the
year and mortality rates. As a result
these estimates can be used in a
straightforward fashion to project
abundance for all ages other than the age
of recruitment (the youngest age in the
model) at the start of next year.
14
trout. The simplest case was for areas
calculated under the assumption of no
phase-in (also called ‘fully phased-in’
areas) and meeting Consent Decree
mortality rate and allocation standards:
MM-5, MM-67, MH-2, MI-5, MI-6, and
MI-7.
Additionally, MH-1 was
considered partially phased-in. This was
accomplished by setting the multipliers
for the recreational and commercial
fisheries so as to simultaneously meet
the mortality target (expressed in terms
of SSBR) and the designated allocation.
The process of finding the correct
multipliers was expedited by making use
of the Solver utility within Microsoft
Excel spreadsheets. In MM-5 the target
mortality rate was 45% and the
allocation was 60% state and 40% tribal.
In MM-67 the target mortality rate was
40% and the allocation was 90% state,
10% tribal. In MH-1, the interim target
mortality was 47%, and the allocation
was 8% state and 92% tribal. In MH-2
the target mortality rate was 40% and the
allocation was 95% state and 5% tribal.
In MI-5 the target mortality rate was
45% and the allocation was 95% state
and 5% tribal. In MI-6 the target
mortality rate was 45% and the
allocation was 50% state and 50% tribal.
In MI-7, the target mortality rate was
45% and the allocation was 30% state
and 70% tribal
In the Lake Superior units
adjustments were made as appropriate
when reporting yield limits to account
for the harvest of hatchery lake trout
since tabled yield limits were taken as
applying to all lean lake trout (wild and
hatchery). This was necessary because
hatchery lake trout, which were not part
of the modeled population, do constitute
a portion of the reported yields. The
recommended yield limits do not include
siscowet lake trout. Sport fishery harvest
In these calculations, background
natural mortality (M) was left at the
same value as was used or estimated in
the SCAA assessments. Although this
was calculated as the average rate in
recent years in most of the projection
sheets, currently M was assumed
constant over time in the assessment
models. Likewise, sea lamprey-induced
mortality was set to the average of the
values in the last three years of the
SCAA.
Fishing mortality rates by type
(either sport and commercial or trap-net
and gill-net for lake trout and lake
whitefish respectively) were based on
average rates in recent years. These
average rates were adjusted to account
for changes stipulated in the Consent
Decree or known changes in fishing
activity by multiplying the baseline agespecific rates by an appropriate
multiplier. For example, if a gill-net
fishery existed in an area prior to 2003,
but did not in 2003, then in projecting
whitefish yield the multiplier for gill-net
fishery was set to zero. When fishing
mortality was adjusted to account for a
specified change in fishing effort, or
when fishing effort was calculated to
correspond with a specific level of
fishing mortality rate, effort and fishing
mortality were treated as being directly
proportional. This basic approach to
fishing mortality assumes that selectivity
and catchability for each source will
remain the same as it was on average in
recent years. Detail on how fishing
mortality rates were adjusted is covered
in the next section.
Setting Fishing Mortality Rates for 2003
Fishing mortality rates were adjusted
depending on specific details of how an
area was designated in the Consent
Decree. We begin by considering lake
15
90% tribal).
Second, TACs were
calculated using a phase-in approach that
is based on the previous years’ harvest,
less the reduction in lake trout harvest
projected from gill-net reductions.
Finally TACs were calculated assuming
the tribal TAC would be 450,000
pounds. Then, the largest tribal TAC
among these three options was chosen.
The state TAC was estimated as though
the model were fully phased-in. Thus
for the second and third option we
followed the same approach as we used
in other areas (i.e., based on 2000-2002
effort and any regulation change). The
phase-in approach was guided by the
Consent Decree's requirement that the
tribal TAC be set to the 1997-1999
harvest adjusted for any change in effort.
We did this by first calculating a 2003
yield based on no-conversion of gear
(1997-1999 effort) and then calculating
taking into account the proportion of
large-mesh gill net that was converted
(as for phase-in rules in other areas).
TAC estimates for fully phased-in
units MM-5 and MI-7 were calculated as
per the consent decree. The 2003 TACs
for both management units changed by
more than 15% compared to the 2002
TACs. The TAC for MM-5 increased
from last year and the TFC agreed to
accept the higher estimated TAC. The
2003 TAC for MI-7 decreased by more
than 15% and the TFC agreed to accept
the limit (15 % less than the 2002 TAC)
as stipulated by the decree instead of the
estimated TAC.
Lake whitefish recommended yields
were calculated generally following the
approach used for fully phased-in lake
trout areas. Details differed because of
the different way that target mortality
was defined for whitefish, and because
for most areas there was no specified
allocation between state and tribal
was reported for lean lake trout. In MI5, commercial yield was reported
separately for lean lake trout. In MI-6
and MI-7 reported commercial yield
included both lean and siscowet lake
trout. The lean-siscowet composition
was
measured
in
commercial
monitoring. Thus total yield can be
114% and 135% of the recommended
yield limits for lean lake trout that we
table. (Note that the harvest and survey
data were adjusted so it reflected only
lean, wild fish before they were
compared with model predictions.)
The TAC for MM-4 was calculated
under a phase-in of effort guidelines for
commercial
effort,
recreational
regulations, and associated harvest
limits. The base period for commercial
effort was 1997-1999.
Hence we
adjusted the average commercial fishing
mortality rates during that period by
multiplying them by the proportion of
1997-1999 large-mesh gill-net effort that
was remaining after conversion of gillnet fishers to trap nets. Recreational
effort was the average of 2000-2002
values, adjusted for any change in size
limits. There was no change in size limit
for MM-4 during 2002, however, the
size limit increased to 22” in 2003.
Commercial TACs were based on
predicted kill adjusted to account for any
The
estimated
under-reporting.
allowable commercial yield was greater
than the 20% change allowed in the
Consent Decree, and the TFC agreed to
accept the higher estimated TAC.
TAC calculations for MM-123 were
more complicated than for other areas
because of special provisions in the
Consent Decree. Potential TACs were
calculated three ways. First, TACs were
calculated assuming that target mortality
rates and allocation were fully phased in
(40% mortality, Allocation 10% state:
16
and Lake Whitefish Populations in the
1836 Treaty-Ceded Waters of Lakes
Superior, Huron and Michigan in 2000,
with recommended yield and effort
levels for 2001. Technical Fisheries
Committee, 1836 Treaty-Ceded Waters
of Lakes Superior, Huron and Michigan.
fisheries (WFS-05 was an exception). In
cases where there was no specified
allocation, the first step was to adjust the
multipliers for trap nets and gill nets to
account for known changes in fishing
effort (generally changes expected to
arise from conversions or movement of
operations). This step merely adjusts the
relative contributions of the two gears.
Then an overall multiplier (that applied
to both gears) was adjusted until the
target mortality rate was reached for the
fully-selected age. When an allocation
was specified the multipliers for the two
gears were adjusted simultaneously (as
was the case for lake trout) to match
both mortality and allocation targets. At
this point SPR was examined and if
below 0.20 the fishing multiplier was
reduced until SPR reached 0.20.
Pauly, D.
1980.
On the
interrelationships
between
natural
mortality, growth-parameters, and mean
environmental-temperature in 175 fish
stocks. Journal du Conseil 39: 175-192.
Sitar, S.P., Bence, J.R., Johnson, J.E.,
Ebener, M.P., Taylor, W.W. 1999.
Lake trout mortality and abundance in
southern Lake Huron. N. Am. J. Fish.
Manage. 19: 881-900.
Spangler, G.R., Robson, D.S., and
Reiger, H.A. 1980. Estimates of
lamprey-induced mortality in whitefish,
Coregonus clupeaformis. Can. J. Fish.
Aquat. Sci. 37:2146-2150.
References cited:
Bence, J.R. 2002. Stock Assessment
Models in Bence J.R. and Ebener, M.P.
(eds.). Summary Status of Lake Trout
17
RECOMMENDATIONS AND FUTURE DIRECTIONS TO
IMPROVE ASSESSMENTS
Prepared by Aaron P. Woldt, James R. Bence, and Mark P. Ebener
In 2002, the MSC revised its list
of recommendations to improve stock
assessments. The revised list reflects
improvements
made
since
the
assessments used to determine 2001
harvest limits, ongoing work to address
assessment needs, and a prioritized
ranking (HIGH, MEDIUM, LOW) of
recommendations.
iii. the extent of discarding by
commercial fisheries
In 2002, CORA submitted a
study plan to the TFC for
calculating the number of lake
trout
discards
in
the
commercial fishery in MH1.
This plan could be used for
other management units where
necessary.
Data collection and processing
• Accurate and complete data on
extractions and other deaths
caused by fishing is essential if
SCAA models are to produce
reliable estimates. The MSC
assigned a HIGH priority to
determining the following:
iv. the significance of recreational
fishing for lake whitefish
In 2002, Michigan compiled
data
showing
yearly
recreational harvest of lake
whitefish in Treaty waters.
After reviewing these data the
MSC determined that harvest
was large enough in WFH03,
WFM05, WFS05, and WFS06
to include in assessment
models. The MSC also asked
Michigan if it would be
possible to conduct more
winter creel surveys in Treaty
waters to estimate lake
whitefish harvest in the ice
fishery, especially in the above
units.
i. the significance of subsistence
fishery harvests
Tribes have made strides in
tracking this harvest, but more
work is needed to better
quantify this harvest for
inclusion in models.
ii. the magnitude of underreporting of lake trout in
commercial fisheries
CORA now compares all tribal
catch and wholesale reports
and updates catch reports to
match the wholesale reports.
This may make the underreporting vector in the models
unnecessary for recent years’
data.
v. the magnitude of recreational
catch
and
release
and
associated hooking mortality
In 2002, Michigan began
modifying its creel program to
18
delineate lake whitefish stock
boundaries.
quantify released lake trout of
both legal and non-legal size.
Also in 2002, the MSC
appointed a subcommittee to
draft a study design to quantify
hooking mortality.
In the
future, the MSC will use creel
catch and release estimates
along with the hooking
mortality to better quantify
discard mortalities in the
recreational fishery.
•
Accurate prior estimates of M
(natural mortality) are essential
in SCAA models.
Existing
tagging information and current
estimates of natural mortality for
lake trout and lake whitefish
need to be reviewed and new
tagging studies designed as
needed. The MSC assigned a
HIGH
priority
to
this
recommendation.
Two basin-wide lake whitefish
tagging studies in lakes Michigan
and Huron have been funded
starting in 2003 and will help
yield estimates of M.
•
The basis for stock boundaries
and assumed movement or lack
of movement between stocks
needs further study. For lake
trout the assumption that stocked
fish move to an area and then
become resident needs to be
evaluated. The MSC assigned a
HIGH
priority
to
this
recommendation.
Two basin-wide lake whitefish
tagging studies in lakes Michigan
and Huron have been funded
starting in 2003 and will help
19
•
We recommend the development
of a consistent protocol for
sampling, processing, and storing
data. The approaches by which
data used in the models were
collected and processed need to
be carefully and completely
documented. The MSC assigned
a HIGH priority to this
recommendation.
•
Last year’s report identified the
need for lake whitefish “indices
of abundance” based on fishery
independent survey data. The
MSC developed a sampling
protocol for lake whitefish that
was implemented on all lakes in
2002. Conducting this survey
and incorporating its results into
the lake whitefish models
continues to be a HIGH priority
for the MSC.
•
Improved
approaches
for
estimating the most recent year's
lake trout yield need to be
investigated.
At the time
assessment
models
are
constructed, final yearly harvest
estimates are not available
because
commercial
catch
reports have not all been turned
in.
In 2002, CORA began
providing the MSC with
projected year end lake trout
harvest for the most recent year
based on patterns in historic
harvest data. The reliability of
this approach needs to be
evaluated. The MSC assigned a
HIGH
priority
to
this
recommendation.
conversions of length-specific
sea lamprey mortality to agespecific rates both depend upon
the coefficient of variation (CV)
in lengths about the mean length
at age. Currently this CV is
assumed to be the same for all
ages and stocks. The validity of
this assumption needs to be
assessed. The MSC assigned a
LOW
priority
to
this
recommendation.
Both CORA and Michigan are
exploring ways to speed up the
processing of commercial catch
reports.
•
Currently lake trout relative
abundance indices (CPUE) used
in SCAA models are preprocessed outside the models
using mixed-model analysis.
The assumptions underlying
these mixed-models need to be
reviewed and improvements
made when appropriate. The
MSC assigned a MEDIUM
priority to this recommendation.
Models
• All lake trout models should
account for sport fishery hooking
mortality. The models should
integrate
hooking
mortality
parameters or include creel
survey estimates of deaths due to
hooking mortality. The MSC
assigned a HIGH priority to this
recommendation.
A graduate student at Michigan
State University (MSU) is
currently exploring this issue.
•
In Lake Michigan sea lamprey
mortality rates are based on fall
(instead of spring) marking and
are based on rates summarized
for broad length categories of
lake trout. The approach used on
the other lakes (using spring data
and estimating wounding as a
function of length) should be
adopted when possible. Spring
wounding data are now being
collected in Lake Michigan. The
MSC assigned a MEDIUM
priority to this recommendation.
•
Estimates of uncertainty for all
data used in models should be
estimated when possible. The
MSC assigned a MEDIUM
priority to this recommendation.
•
For lake trout, calculations of the
effects of recreational fishery
size limit regulations and
•
20
The overall approach in the
SCAA models to estimate fishery
selectivity needs to be evaluated,
and
alternative
approaches
should be considered. Currently
the models use either a single or
double logistic function of age.
Alternative
age-specific
functions should be considered.
Furthermore, some of the SCAA
models
have
time-varying
selectivity by assuming that one
of the selectivity parameters
varies over time following a
polynomial function. Alternative
approaches (such as using a
random walk for this variation)
should be evaluated. The MSC
assigned a MEDIUM priority to
this recommendation.
harvested for comparison with
SCAA model predictions needs
to be reviewed. The current
approach is to divide annual
reported fishery yield by the
annual average weight of a
harvested fish.
The average
weight of a harvested fish is
poorly estimated in some years.
An alternative is to convert
predicted numbers harvested to
yield based on weight-at-age
data, which may be a better
estimate. The MSC assigned a
MEDIUM priority to this
recommendation.
A graduate student at MSU is
currently exploring this issue.
•
The assumption that fishery and
survey catchability is constant in
the SCAA models needs to be
evaluated. Alternatives include
allowing catchability to vary over
time following a random walk or
in response to population density.
The MSC assigned a MEDIUM
priority to this recommendation.
A graduate student at MSU is
currently exploring this issue
•
Alternative
approaches
to
weighting likelihood components
needs to be reviewed. It is
possible that some weighting
factors could be improved using
other statistical approaches. The
MSC assigned a MEDIUM
priority to this recommendation.
•
A graduate student at MSU is
currently exploring this issue
•
Current approaches to modeling
and estimating recruitment need
to be reviewed.
The MSC
assigned a MEDIUM priority to
this recommendation.
•
Current harvest policies and
possible alternatives should be
evaluated
using
stochastic
simulations that use information
from the SCAA assessment
models and from published and
unpublished studies. The MSC
assigned a MEDIUM priority to
this recommendation.
•
The
age-specific
maturity
schedules are assumed to be
temporally constant in lakes
Michigan and Huron lake trout
models. Alternative approaches
that allow temporal changes due
to changes in growth should be
evaluated. The MSC assigned a
MEDIUM priority to this
recommendation.
Reporting and Time Frames
The current time frame for
calculating lake trout harvest limits is
very narrow and does not allow adequate
time for model evaluation given the
constraints of data availability. The time
frame for lake whitefish quotas is a year
longer than for lake trout and is
sufficient.
The timing of data
availability and target dates for delivery
can be summarized as:
Lake Trout
The Consent Decree sets the overall
deadline for data availability for lake
trout at March 1. The MSC moved this
date to February 15 to allow additional
time to run the SCAA models and
The procedures to convert fishery
yield to numbers of fish
21
4. Stocking data:
These data are provided by the
USFWS and are available by
February 15.
calculate harvest limits. The MSC also
set the second full week in March for its
annual meeting to produce preliminary
lake trout harvest limits. This allows
time for group discussion of model
output and diagnostics before the March
31 deadline for preliminary harvest
limits.
There is some difficulty with the data
submission deadline as sometimes data
needs extensive processing before it can
be used in the models. Issues associated
with individual data sources and plans
for improving timeliness of assessments
include:
5. Survey data:
a. Survey CPUE – These data can
be ready by February 15. Often
the mixed model analysis can be
completed by February 15. We
will use a general linear model to
estimate CPUE.
b. Age composition – These data
can be ready by February 15,
except occasionally in Lake
Superior.
If not ready by
February 15, we will proceed
without the most recent year's
data.
1. Harvest/Yield:
a. Commercial yield - Currently
CORA and the State cannot be
ready by February 15. These
numbers need to be made
available in a more timely and
accurate fashion.
c. Mean length and weight at age –
These data can be ready by
February 15 and the estimates of
von Bertalanffy model can be
updated by February 15.
b. Recreational harvest – the State
can provide these data by
February 15.
d. Sea lamprey marking – These
data can be ready by February 15
and estimates of mortality can be
ready by February 15.
2. Biological data-commercial:
These data can be available by
February 15.
We use age
composition, mean weight in harvest,
mean length at age, and composition
of siscowets, wild and hatchery fish.
e. Maturity at age – These data can
be ready by February 15. These
are constants in lakes Huron and
Michigan and vary in Lake
Superior.
3. Biological data-recreational:
These data can be available by
February 15. Occasionally Lake
Superior data are not available by the
deadline. If not ready by March 1
we will proceed without it and use
the data the next year. We use age
composition, mean weight of
harvested fish, and composition of
wild and hatchery fish.
Lake whitefish
The Consent Decree sets October 1
as the deadline for the previous year’s
data. The MSC moved this deadline to
September 1 to allow additional time for
calculating harvest limits. Because of
the one year time lag, data are usually
available by the data submission
22
deadline. The MSC also set the third
full week in September for its annual
meeting to produce preliminary lake
whitefish harvest limits. This allows for
group discussion of model output and
diagnostics before the November 1
deadline for preliminary harvest limits.
More general comments
• The MSC recommends that in
addition to this status of the
stocks report (termed short
report), a second report for the
2001 assessments be written that
documents and describes in detail
the modeling methods used
(termed long report). The 2001
long report is currently being
written.
We recommend the
short report be produced annually
and include text describing any
changes in the modeling process
for a given management unit and
species. The long report will be
produced periodically following
substantial changes in methods
used to produce harvest limits.
•
The MSC is concerned about the
short time frame between data
availability and the deadline for
lake trout harvest limits. The
time period between the data
submission deadline and the
deadline for preliminary harvest
limits is too narrow to allow
sufficient
model
analysis,
diagnostics
of
model
convergence, and estimation of
harvest limits. Given the life
history of lake trout, it may be
reasonable to either update the
lake trout models every 2-3 years
or update them with a one-year
lag for some data sources.
23
•
The lake whitefish models need
to be updated annually. It would
be more efficient if the date by
which the results were due was
moved forward to March 31, to
correspond with the lake trout
deadline (e.g. harvest limits
based on 2002 data would be
reported on March 31, 2004
instead of November 1, 2003).
•
Age
composition
and
commercial yield are the data
that generally limit producing
timely results. Above we have
suggested an approach for
providing commercial yield data
sooner.
In some areas age
compositions may not be
available when harvest limit
calculations
begin;
we
recommend proceeding without
the most recent year's data in
these cases.
STATUS OF LAKE TROUT POPULATIONS
Lake Superior
MI-5 (Marquette - Big Bay)
Prepared by Shawn P. Sitar
on the sport fishery, though most of the
fishery occurs during the months of May
through October. Recreational harvest
of wild lake trout has increased from
4,400 fish (39,800 lb) in 1986 to a peak
of 15,000 fish (67,500 lb) in 1997 and
has averaged 12,100 fish (47,000 lb) per
year during the last five years.
Recreational effort has declined from
146,000 angler hours in 1986 to 56,000
angler hours in 2002.
Lake trout management unit MI5 extends from Pine River Point (west of
Big Bay) to Laughing Fish Point (east of
Marquette), covering 374,096 hectares.
The management unit includes Stannard
Rock, an offshore shoal about 72 km
north of Marquette, and is in both the
1836 (250,345 hectares) and 1842 Treaty
waters (123,751 hectares). The 1836
Treaty waters extend east from the
north-south line established by the
western boundaries of grids 1130, 1230,
1330, 1430, and 1530. This unit has a
wide bathymetric range with depths
down past 240 meters, and with 75,600
hectares with bottom depths of 73.2 m
(240 ft) or less.
The only tribal commercial
fishery is a large-mesh gill-net fishery
that is centered around Marquette and
Big Bay in 1842 Treaty waters. This
fishery mainly targets lake whitefish
with lake trout as bycatch. There have
been some low levels of tribal
subsistence gill-net fishing in 1836
treaty waters. Tribal commercial yield
of wild lake trout (in 1842 treaty waters)
has ranged from 3,100 lb in 1986 to a
peak of 42,100 lb in 2000. During 1998
to 2002, tribal yield averaged 20,800 lb
and tribal large-mesh gill-net effort
averaged 365,000 ft per year.
Recreational harvest of lake trout
comprises both charter and sport angler
trolling. Most of this activity is centered
around the port of Marquette, though
some lake trout are harvested at Stannard
Rock. There are no seasonal restrictions
Commercial and recreational fishery lake trout harvest MI-5
160
140
120
Recreational
Commercial
TAC
100
80
60
40
20
0
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
Year
Abundance of age-3 and older wild
lake trout increased over two-fold since
1975 and has recently declined from a
peaked of about 1.3 million fish in 1988.
Total biomass of age-3 and older lake
trout averaged 2.8 million lb (1.3 million
kg) during 1993-2002.
Lake trout
biomass declined from 4.3 million lb (2
million kg) in 1990 to 2 million lb
(900,000 kg) in 2002. Spawning stock
biomass averaged 446,000 lb (202,000
kg) during 1993 to 2002. Although lake
trout abundance has increased since the
mid-1970s, spawning stock biomass has
declined due to significant decreases in
growth. This is likely to continue with
24
the Consent Decree, allocating 40 % of
the total yield to 1836 waters. Within
1836 waters, the recommended yield is
allocated 95% to the state and 5% to the
tribes. Note that this yield limit applies
to wild and hatchery lake trout caught,
whereas target mortality rates apply only
to wild lean lake trout. In recent years
wild lean lake trout compose
approximately 90% of the total yield.
The recommended limit exceeds recent
yields in 1836 Treaty waters (e.g., an
average of 73,100 lb during 2000-2002),
reflecting the fact that recent mortality
rates have been well below target rates.
declines in growth and increases in
mortality rates.
Estimated lake trout abundance MI-5
1400
Age 3
1200
Ages 3 to 15 pooled
1000
800
600
400
200
0
Year
Estimated lake trout biomass in MI-5
4500
4000
Total
Spawning Stock
3500
Instantaneous mortality rates for lake trout ages 6-11 in MI-5
3000
0.45
2500
Natural
Commercial
Recreational
Sea Lamprey
0.4
2000
0.35
1500
0.3
1000
0.25
0.2
500
0.15
0
0.1
1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
0.05
Year
0
During 1975 to 2002, sea lampreyinduced mortality was the dominant
mortality source, although mortality
from this source has declined since the
mid-1980s. With the exception of 1988
and 2000, recreational fishing mortality
has been higher than commercial fishing
mortality since 1986. Average total
annual mortality (A) for ages 6-11 lake
trout has declined from 31% during 1975
to 1978 to 28% during 2000 to 2002.
Spawning stock biomass produced per
recruit during 2000 to 2002 has been
above the target value indicating that
mortality rates are low and there is good
population reproductive potential. The
recommended yield limit for 1836
Treaty waters was 119,100 lb, allocated
as 113,600 lb for the state recreational
fishery and 5,500 lb for the tribal
commercial/subsistence fishery. This
recommended yield limit is based on the
target mortality rate of 40% defined in
Year
25
Summary Status MI-5 Lake Trout
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
2.38 lb
6y
4.33 lb
10 y
Spawning biomass per recruit
Base SSBR
3.689 lb
(SE 0.455)
0.97 lb
(SE 0.12)
0.509 lb
(SE 0.019)
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
0.264
(SE 0.020)
Average yield per recruit
0.450 lb
(SE 0.056)
Natural Mortality (M)
0.177 y
Fishing Mortality
Age of full selection
Commercial Fishery (2000-2002)
Age of full selection
Sport fishery (2000-2002)
Commercial Fishing mortality (F)
(average 2000-2002, ages 6-11)
-1
15
9
-1
0.026 y
(SE 0.005)
Sport fishery F
(average 2000-2002, ages 6-11)
-1
0.042 y
(SE 0.007)
Sea lamprey mortality (ML)
(average ages 6-11,2000-2002)
0.084 y
-1
Total mortality (Z)
(average ages 6-11,2000-2002)
Recruitment (age-3)
(1993-2002 average)
-1
0.329 y
(SE 0.015)
189,690 fish
(SE 32,022)
Biomass (age 3+)
(1993-2002 average)
2,791,400 lb
(SE 365,800)
Spawning biomass
(1993-2002 average)
445,460 lb
(SE 60,995)
MSC recommended yield limit for 2003
Actual yield limit for 2003
26
119,100 lb
119,100 lb
MI-6 (Au Train - Munising)
Prepared by Shawn P. Sitar
lean lake trout. The remainder was of
hatchery origin. Recreational effort has
declined from 72,000 angler hours in
1988 to 41,000 angler hours in 2002.
Lake trout management unit MI6 extends from Laughing Fish Point
(east of Marquette) to Au Sable Point
(east of Munising), encompassing 1.8
million acres. The management unit
includes Big Reef, an offshore reef
complex about 20 mi northeast of
Munising. This management unit
contains the deepest waters of Lake
Superior with soundings deeper than
1,400 ft, and only 185,000 acres of the
total area is shallower than 240 ft.
The commercial fishery that
harvests lake trout is a tribal large-mesh
gill-net fishery that is centered east of
Grand Island.
This fishery mainly
targets lake whitefish with lake trout as
bycatch. Tribal commercial yield of
wild lake trout peaked in 1989 at 25,600
lb and declined to an average of 7,300 lb
during 1998 to 2002. In addition to wild
lean lake trout the tribal fishery also
harvests siscowet and hatchery lake
trout.
In recent years wild fish
composed 78% of the total lake trout
yield, with 13% siscowet and 7%
hatchery fish. Tribal large-mesh gill-net
effort decreased from a peak of 3.6
million ft in 1983 to 487,000 ft in 2002.
Recreational harvest of lake trout
comprises fish caught by both charter
and sport angler trolling. Most of the
recreational harvest was from the Au
Train Bay and Grand Island areas,
although some harvest was also from
Big Reef. Recreational harvest of wild
lake trout has increased from 970 fish
(5,100 lb) in 1987 to 5,300 fish (17,800
lb) in 2002 and averaged 4,200 fish
(18,000 lb) per year since 1987. In the
last five years, wild lake trout composes
93% of the total recreational harvest of
Commercial and recreational fishery lake trout harvest MI-6
60
Recreational
Commercial
TAC
50
40
30
20
10
0
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
Year
Abundance of age-4 and older wild
lake trout declined from 350,000 fish in
1989 to 184,000 fish in 2002.
Recruitment at age 4 has declined during
1993-2002 and averaged 58,900 fish
during this period. The decline in
abundance is related to increases in
mortality rates starting in 1996 and
declines observed in recruitment starting
in 1995. Total biomass of age 4 and
older lake trout has averaged 965,600 lb
(438,000 kg) during 1993 to 2002.
Biomass has declined from 1.2 million
lb (540,000 kg) in 1995 to 579,000 lb
(263,000 kg) in 2002. Spawning stock
biomass averaged 126,000 lb (57,200
kg) during 1993 to 2002 and represented
13% of total stock biomass.
27
the Modeling Subcommittee assumed
that 6% of the yield would be hatchery
fish. During 2002, recreational release
of lake trout in MI-6 was measured in
the creel survey. Catch and release
mortality was estimated by multiplying
the creel survey estimates of released
lake trout by 15%, which was based on
Loftus et al. (1988). Reported total
recreational harvest included estimated
harvest and hooking deaths. There were
650 lake trout (2,100 lb) released during
2002.
Estimated lake trout abundance MI-6
450
400
Age 4
350
Ages 4 to 15 pooled
300
250
200
150
100
50
0
Year
Estimated lake trout biomass in MI-6
1400
1200
Total
Spawning Stock
Instantaneous mortality rates for lake trout ages 6-11 in MI-6
0.9
1000
Natural
Commercial
Recreational
Sea Lamprey
0.8
800
0.7
600
0.6
0.5
400
0.4
0.3
200
0.2
0
0.1
1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
0
Year
Year
Excluding
background
natural
mortality, sea lamprey predation was the
highest mortality source for age 6 to 11
lake trout in MI-6. Recreational fishing
mortality has been higher than
commercial fishing mortality since 1991.
During 1978 to 2002, total annual
mortality (A) was the highest in 1979 at
57% and declined to 23% in 1993.
Subsequently, A increased to an average
of 30% during 2000 to 2002.
The MSC recommended yield limit
for 2003 is 50,700 lb of which 27,500 lb
is allocated for state recreational yield
and 23,200 lb for tribal commercial
yield. While mortality rates apply only
to wild lean trout, the yield limit applies
to all lean trout. In calculating the limit
Due to state overharvest in MI-6
in 2002, the TFC applied penalty
provisions outlined in Sections VII.B.4.a
and VII.B.4.b of the Consent Decree and
re-allocated the 2003 harvest limits as
follows: 22,900 lb to the state and
27,800 lb to the tribes.
Addendum: In the 2001 Status of
the Stocks Report we described female
maturity for MI-6 by the length at first
spawning. For the 2002 report, and from
now on, we will use weight at first
spawning so that the same metric is
reported for all units.
28
Summary Status MI-6 Lake Trout
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
2.37 lb
6y
4.38 lb
10 y
Spawning biomass per recruit
Base SSBR
4.816 lb
(SE 0.552)
0.91 lb
(SE 0.09)
0.409 lb
(SE 0.011)
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
0.188
(SE 0.012)
Average yield per recruit
0.386 lb
(SE 0.046)
0.166 y
Natural Mortality (M)
Fishing Mortality
Age of full selection
Commercial Fishery (2000-2002)
Age of full selection
Sport fishery (2000-2002)
Commercial Fishing mortality (F)
(average 2000-2002, ages 6-11)
-1
8
9
-1
0.022 y
(SE 0.004)
Sport fishery F
(average 2000-2002, ages 6-11)
-1
0.046 y
(SE 0.007)
Sea lamprey mortality (ML)
(average ages 6-11,2000-2002)
0.129 y
-1
Total mortality (Z)
(average ages 6-11,2000-2002)
Recruitment (age-4)
(1993-2002 average)
-1
0.363 y
(SE 0.014)
58,849 fish
(SE 6,473)
Biomass (age 4+)
(1993-2002 average)
965,610 lb
(SE 93,219)
Spawning biomass
(1993-2002 average)
125,920 lb
(SE 15,072)
MSC recommended yield limit for 2003
Actual yield limit for 2003
29
50,700 lb
50,700 lb
MI-7 (Grand Marais)
Prepared by Shawn P. Sitar
questionable assumptions, hence there is
much uncertainty regarding the true
magnitude of the recreational harvest in
MI-7 prior to 2001. However, the
residuals between the ratio procedure’s
estimates of harvest and actual creel
survey estimates since 2001 were -16%
(365 fish) in 2001 and 3.1% (76 fish) in
2002.
Lake trout management unit MI7 extends from Au Sable Point (west of
Grand Marais) to Little Lake Harbor
(east of Grand Marais), encompassing
987,000 acres. This management unit
has complex bathymetry with many
lacustrine ridges, trenches, and slopes.
There is approximately 92,000 acres of
lean lake trout habitat (depth less than
240 ft).
The commercial fishery that
harvests lake trout is a tribal large-mesh
gill-net fishery that is mostly based out
of Grand Marais. This fishery mainly
targets lake whitefish with lake trout as
bycatch. During 1975 to 2002, tribal
commercial yield of wild lake trout
peaked in 1990 at 104,400 lb and
declined to 12,400 lb in 1996.
Subsequently, tribal yield increased to an
average of 56,000 lb in the last three
years. In recent years these yields of
wild lean lake trout compose about
53.7% of the total lake trout yield, with
the rest consisting of siscowet (41%) and
hatchery lake trout (5.3%). Tribal largemesh gill-net effort has shown the same
temporal pattern as commercial yield,
with a peak effort of 8.2 million ft in
1990.
The standardized creel survey began
at Grand Marais in 2001. Sport harvest
and effort in MI-7 for years prior to 2001
were estimated using the average sport
CPUE and effort index ratio between
MI-7 to MI-5 from MIDNR creel mail
survey data 1971 to 1982 applied to MI5 sport harvest and effort during 19842000. The estimates from this procedure
indicate that recreational harvests in MI7 are about half those of MI-6. This
procedure required strong and somewhat
Commercial and recreational fishery lake trout harvest MI-7
160
140
120
Recreational
Commercial
TAC
no creel
survey
100
80
60
40
no creel
survey
20
0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Year
Abundance of age-3 and older wild
lake trout averaged 567,000 fish during
1993 to 2002 and has declined from
656,000 fish in 1997 to an average of
466,000 fish in 2002. Recruitment at
age 3 averaged 139,000 fish during 1993
to 2002.
Spawning stock biomass
averaged 86,000 lb during the last ten
years and represented 6.4% of total stock
biomass.
Estimated lake trout abundance MI-7
900
Age 3
Ages 3 to 15 pooled
800
700
600
500
400
300
200
100
0
Year
30
this limit by 41%, to allow for the
portion of the yield that siscowet are
expected
to
compose.
The
recommended total yield limit is higher
than observed yields from recent years
reflecting the fact that mortality rates
have been below target limits.
The
2003
model-generated,
recommended yield limit for this unit is
more than 15% lower than the 2002 final
lake trout harvest limit. As a result, the
TFC invoked Section VII.A.6 of the
Consent Decree and set the 2003 final
harvest limit for this unit to 112,700 lb
of which 33,800 lb was allocated for
state recreational yield and 78,900 lb for
tribal commercial yield. This final 2003
harvest limit is 15% lower than the 2002
final harvest limit.
Estimated lake trout biomass in MI-7
2500
Total
Spawning Stock
2000
1500
1000
500
0
1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Sea lampreys were the dominant
mortality source for lake trout in MI-7
from 1975 to 1989. Commercial fishing
mortality increased significantly in 1985
and exceeded sea lamprey-induced
mortality from 1990 to 1994.
Commercial fishing mortality declined
during 1995 to 1998, but has been
increasing since 1998. During 1975 to
1979, total annual mortality (A) for age6 to -11 lake trout averaged 43.6%.
During the last five years, average A was
34.6%. The current spawning stock
biomass per recruit (SSBR) estimate for
MI-7 is above the target value,
indicating that mortality rates are not
exceeding the target.
The modelgenerated, recommended yield limit for
the year 2003 is 88,300 lb of which
29,800 lb is allocated for state
recreational yield and 58,500 lb for tribal
commercial yield. These limits were
calculated on the basis of the target
mortality rate (A) of 40% and an
allocation of 30% to the state and 70% to
the tribes, in accord with the Consent
Decree. These yield limits apply to all
lean lake trout, but mortality targets only
apply to wild lean lake trout.
In
determination of the yield limit it was
assumed that 11.2% of the lean lake
trout yield would be hatchery fish. The
yield limit does not include siscowet
lake trout so actual yields can exceed
Instantaneous mortality rates for lake trout ages 6-11 in MI-7
0.8
Natural
Commercial
Recreational
Sea Lamprey
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Year
31
Summary Status MI-7 Lake Trout
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
2.77 lb
6y
4.95 lb
10 y
Spawning biomass per recruit
Base SSBR
2.947 lb
(SE 0.397)
0.58 lb
(SE 0.09)
0.421 lb
(SE 0.019)
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
0.196
(SE 0.031)
Average yield per recruit
0.382 lb
(SE 0.095)
-1
Natural Mortality (M)
0.209 y
Fishing Mortality
Age of full selection
Commercial Fishery (2000-2002)
Age of full selection
Sport fishery (2000-2002)
Commercial Fishing mortality (F)
(average 2000-2002, ages 6-11)
13
6
-1
0.081 y
(SE 0.025)
Sport fishery F
(average 2000-2002, ages 6-11)
-1
0.008 y
(SE 0.002)
Sea lamprey mortality (ML)
(average ages 6-11,2000-2002)
-1
0.13 y
Total mortality (Z)
(average ages 6-11,2000-2002)
Recruitment (age-3)
(1993-2002 average)
-1
0.428 y
(SE 0.028)
138,740 fish
(SE 37,438)
Biomass (age 3+)
(1993-2002 average)
1,335,900 lb
(SE 332,860)
Spawning biomass
(1993-2002 average)
86,077 lb
(SE 27,129)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (15% rule invoked)
32
88,300 lb
112,700 lb
Lake Huron
MH-1 (Northern Lake Huron)
Prepared by Aaron P. Woldt and Ji X. He
and covers 177,840 acres of 1836 Treaty
waters. Retention of lake trout in the
refuge is strictly prohibited.
There is little or no natural
recruitment of lake trout in northern
Lake Huron. As a result, nearly all the
lake trout harvest is comprised of
hatchery fish. The United States Fish
and Wildlife Service annually plants
lake trout in MH-1. From 1998 to 2002,
approximately 360,000 yearling lake
trout were planted annually in MH-1.
Under the 2000 Consent Decree,
stocking was increased in MH-1 to
levels prescribed in the Lake Huron
Committee's Lake Trout Rehabilitation
Guide. In 2002, approximately 486,000
yearling lake trout were stocked into
MH-1. After adjusting for post stocking
survival and immigration and emigration
based on coded-wire-tag data, the MH-1
model estimated 443,000 yearling lake
trout recruits in MH-1 for 2002.
Both
commercial
and
recreational lake trout fisheries exist in
MH-1. Tribal commercial fishers deploy
trap nets and large-mesh gill nets (4.5
inch stretch) that target lake whitefish
and salmon, and small-mesh gill nets
(2.5-3.0 inch stretch) that target bloater
chubs. Lake trout are caught in these
fisheries as bycatch and can be marketed
by tribal fishers under CORA
regulations.
No
state-licensed
commercial fishers operate in MH-1.
The Consent Decree prohibits statelicensed commercial fishing north of the
45th parallel. Previous to August 2000
one state-licensed fisher, Gauthier and
Spaulding Fisheries, operated a trap-net
Lake trout management unit MH1 is located in northern Lake Huron and
extends from the Mackinaw Bridge
south to the border between grids 607
and 608, encompassing statistical district
MH-1 and adjacent Canadian waters
(Canadian management area 4-1). The
management unit has a wide bathymetric
range with areas in grids 407 and 408 as
deep as 426 ft. The Michigan portion of
this unit lies completely within 1836
Treaty waters, covering 1,017,640 acres
of which approximately 681,720 acres
are less than 240 feet in depth. On the
Michigan shore this unit encompasses
the ports of Saint Ignace, Mackinaw
City, Cheboygan, Hammond Bay, and
Rogers City. The St. Marys River,
connecting Lakes Superior and Huron,
flows into Lake Huron in grid 306. The
St. Marys River has supported large
spawning runs of sea lamprey, and until
the late 1990’s the resulting larval
populations
were
untreated
and
contributed substantial numbers of
parasitic-phase sea lamprey to the lake.
Comprehensive treatment of the river by
the Great Lakes Fishery Commission's
control agents has reduced the number of
sea lamprey produced in the St. Marys
River, and decreases in lake trout
wounding and sea lamprey-induced
mortality rates are being documented in
northern Lake Huron. The majority of
Lake Huron’s historically important lake
trout spawning reefs and shoals are
located in MH-1. The Drummond Island
Refuge is located in grids 307, the
northern ½ of grid 407, and Michigan
waters of grids 308, 408, 409, and 410,
33
water column. A limited number of
subsistence fishing permits are also
issued to tribal members in 1836 Treaty
waters. Recreational harvest represents
a small portion of the total fishery
harvest in MH-1. From 1998 to 2002,
recreational yield of lake trout averaged
4,600 lb. In 2002, recreational harvest
was only 3,100 lb in MH-1. Starting in
2001, the state of Michigan raised the
minimum size limit for lake trout in the
recreational fishery from 10” to 20” in
areas north of 44° 50’ N latitude.
Starting in 2003, the state of Michigan
imposed a 15” to 19” slot limit in MH-1.
All fish outside the slot must be released,
except for one fish daily that may be 34”
or larger. These new regulations are
intended to keep harvest below the state
share of the MH-1 harvest limit.
operation in MH-1. This operation
targeted lake whitefish and was not
allowed to market lake trout bycatch.
All lake trout were returned to the water,
regardless of condition.
Because there is a substantial
commercial fishery for lake trout in
Canadian waters adjacent to MH-1,
although few lake trout have been
stocked there, this region was included
in the assessment model. This means
that lake trout extractions from Canadian
management area 4-1 were included in
the data, and estimates of yields and
recruitment into this area (primarily the
result of movement from other areas)
were also included. From 1998 to 2002,
tribal commercial yield of lake trout
averaged 105,000 lb, while Canadian
commercial yield averaged 19,000 lb.
Due to a 400 lb daily bag limit enacted
by CORA for tribal large-mesh gill-net
fishers in US waters of MH-1, 2002
tribal harvest includes an estimate of
throwback mortality (i.e. fish that were
thrown back but later died due to
handling). The majority of tribal lake
trout yield (89%) came from the largemesh gill-net fishery. Tribal large-mesh
gill-net effort averaged 10.4 million ft
from 1998 to 2002, while Canadian
large-mesh gill-net effort averaged 1.9
million ft. With the implementation of
the 2000 Consent Decree, tribal largemesh gill-net catch and effort is
declining. In 2002, large-mesh gill-net
harvest dropped by 18,000 lb from 2000,
and large-mesh gill-net effort dropped
by 7.1 million feet from 2000.
The state-licensed recreational
fishery in MH-1 is composed of both
charter and non-charter anglers. Lake
trout are frequently caught as bycatch by
salmon anglers trolling at or near the
surface, but some anglers target lake
trout by fishing the lower parts of the
Harvest of lake trout by fishery
250
200
Recreational
Commercial
150
100
50
0
1977 1980 1983 1986 1989 1992 1995 1998 2001
Year
Instantaneous mortality rates
have been variable and relatively high in
northern Lake Huron. From 1977 to
1990, commercial fishing mortality was
the leading source of lake trout
mortality.
After 1990, commercial
fishing mortality decreased as sea
lamprey-induced mortality increased.
Sea lamprey were the largest source of
lake trout mortality in the 1990s, until
1998 when sea lamprey-induced
mortality decreased. From 1998 to
2002, lamprey-induced instantaneous
mortality averaged 0.15 y-1 and
commercial
fishing
instantaneous
Sea
mortality averaged 0.22 y-1.
34
percentage (92% for tribal harvest and
8% for the state) as outlined in Section
VII.A.7.d of the Consent Decree. Based
on these calculations, the total yield was
allocated 15,300 lb to the state and
147,000 lb to the tribes. Due to tribal
overharvest in MH-1 in 2002, the TFC
applied penalty provisions outlined in
Sections VII.B.4.a and VII.B.4.b of the
Consent Decree and re-allocated the
2003 harvest limits as follows: 31,800
lb to the state and 131,200 lb to the
tribes.
The 2001 harvest limit was
calculated based on the phase-in
described in the Consent Decree. In
particular, it was based on the average
effort during 1997 to 1999, either
adjusted for gill-net operations converted
to trap nets under provisions of the
Consent Decree (tribal commercial
fishery) or changes in regulations (state
recreational fishery).
The Consent
Decree states that this technique should
be used to calculate the MH-1 harvest
limit through 2005. However, due to
changes in lake trout stock dynamics in
MH-1 caused by larger than expected
decreases in sea lamprey-induced
mortality, calculating the 2002 and 2003
harvest limits using the phase-in method
described in the Decree results in
projected total annual mortality rates that
fall below the target specified in the
Decree.
In February 2003 the Executive
Council of the 2000 Consent Decree
instructed the MSC to calculate lake
trout harvest limits using interim total
annual mortality rates in units where
conformity to Consent Decree provisions
resulted in harvest limits based on total
annual mortality rates below target.
Model projections indicate that
harvest reductions due to gill-net
conversion
and
more
stringent
lamprey-induced mortality rates for age
6-11 lake trout in 2002 decreased 77%
from the average of 1994-1998 levels.
This decline is likely due to the
treatment of the St. Marys River.
Recreational fishing mortality was low
in all years relative to commercial
fishing mortality in northern Lake
Huron.
Instantaneous mortality rates (age 6-11)
2.5
Recreational
Commercial
Lamprey
Natural
2.0
1.5
1.0
0.5
0.0
1977 1980 1983 1986 1989 1992 1995 1998 2001
Year
High rates of both sea lampreyinduced and commercial fishing
mortality caused the age structure in
northern Lake Huron to be truncated just
before the age of first maturity. As a
result, spawning stock biomass (SSB) is
extremely low in northern Lake Huron,
and total lake trout biomass varied
around a 20-year average of 1,111,100
lb.
Lake trout biomass and SSB in MH-1
2,000
1,500
Total Biomass
SSB
1,000
500
0
1977 1980 1983 1986 1989 1992 1995 1998 2001
Year
The Modeling Subcommittee of
the TFC recommends a lake trout
harvest limit of 163,000 lb for MH-1 in
2003. This harvest was calculated using
the interim-target total annual mortality
rate of 47% and 2006 allocation
35
recreational fishing regulations, along
with reductions in sea lamprey mortality
due to the treatment of the St. Marys
River, should allow the lake trout
population in MH-1 to progress towards
rehabilitation.
Tribal harvest was significantly
higher than the tribal harvest limit in
2002, but still represented a decline in
harvest from previous years.
State
harvest was well below the state harvest
limit in 2002. The total harvest limit
increased 67,600 lb from 2002 to 2003.
Yearly harvest and harvest limits
180,000
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
Tribal Harvest
State Harvest
Harvest Limit
2001
2002
Year
2003
36
Summary Status MH-1 Lake Trout
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
3.33 lb
5y
5.94 lb
8y
Spawning biomass per recruit
Base SSBR
2.395 lb
(SE 0.25)
0.24 lb
(SE 0.06)
0.284 lb
(SE 0.013)
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
0.099
(SE 0.022)
Average yield per recruit
0.566 lb
(SE 0.035)
0.224 y
Natural Mortality (M)
Fishing Mortality
Age of full selection
Commercial Fishery (2000-2002)
Age of full selection
Sport fishery (2000-2002)
Commercial Fishing mortality (F)
(average 2000-2002, ages 6-11)
-1
6
7
-1
0.208 y
(SE 0.048)
Sport fishery F
(average 2000-2002, ages 6-11)
-1
0.005 y
(SE 0.001)
Sea lamprey mortality (ML)
(average ages 6-11,2000-2002)
0.113 y
-1
Total mortality (Z)
(average ages 6-11,2000-2002)
Recruitment (age-1)
(1993-2002 average)
-1
0.55 y
(SE 0.052)
365,960 fish
(SE 25,050)
Biomass (age 3+)
(1993-2002 average)
1,329,200 lb
(SE 103,920)
Spawning biomass
(1993-2002 average)
28,195 lb
(SE 6,340)
MSC recommended yield limit for 2003
Actual yield limit for 2003
37
163,000 lb
163,000 lb
MH-2 (North-central Lake Huron)
Prepared by Aaron P. Woldt and Ji X. He
Island, North Point, and Six Fathom
Bank. The Six Fathom Bank Refuge is
located in the eastern half of grids 913
and 1013, grids 914 and 1014, and
Michigan waters of grids 915 and 1015
covering 251,940 acres.
Canadian
waters adjacent to the refuge are a
commercially protected area where
commercial fishers are prohibited from
fishing in waters shallower than 40
fathoms.
Recreational anglers may
harvest lake trout in Canadian waters
adjacent to the refuge, but few, if any,
travel the long distance offshore.
Approximately ½ of the refuge lies in
MH-2 (118,560 acres), and retention of
lake trout in the refuge is strictly
prohibited.
There is little or no natural
recruitment of lake trout in north-central
Lake Huron. Only one site off North
Point has yielded consistent, yearly
production of wild juvenile lake trout in
MH-2 since 1985, but trawl catches at
this site have disappeared in recent
years. As a result, nearly all lake trout
harvest is comprised of hatchery fish.
The United States Fish and Wildlife
Service annually plants lake trout in
MH-2.
From 1998 to 2002,
approximately 280,000 yearling lake
trout per year were planted annually in
near-shore areas of MH-2. For the first
time since 1987, no lake trout were
planted offshore on Six Fathom
Bank/Yankee Reef in 2002. These fish
were re-allocated to nearshore stocking
sites and may return to the mid-lake
reefs as part of a pulse stocking regime
being considered by the Lake Huron
Technical Committee. Approximately
Lake trout management unit MH2 is located in north-central Lake Huron.
It includes statistical district MH-2
(grids 409-410, 509-512, 608-614, 709715, 809-815, and 909-915 for a total of
1,521,520 acres) as well as adjacent
Canadian waters (areas 4-2, 4-3, and 4-7
for a total of 1,526,460 acres). Michigan
waters of the MH-2 unit include both
1836 Treaty waters (723,710 acres) and
non-treaty waters (797,810 acres),
divided by a line running north-east from
the tip of North Point to the international
border. The Michigan ports of Presque
Isle and Alpena are contained in this
unit. The St. Marys River, connecting
Lakes Superior and Huron, flows into
northern Lake Huron in grid 306, to the
north of this unit. The St. Marys River
has supported large spawning runs of sea
lamprey, and until the late 1990’s the
resulting larval populations were
untreated and contributed substantial
numbers of parasitic phase sea lamprey
to the lake. Comprehensive treatment of
the river by the Great Lakes Fishery
Commission's control agents has
reduced the number of sea lamprey
produced in the St. Marys River, and
decreases in lake trout wounding and
sea-lamprey induced mortality rates are
being documented in northern Lake
Huron. The management unit has a wide
bathymetric range, with areas in grids
714 and 814 deeper than 690 feet, and a
total of 202,540 acres of 1836 Treaty
waters with bottom depths of 240 feet or
less. This management unit contains a
limited number of historically important
lake trout spawning reefs and shoals.
These reefs are located near Middle
38
salmon anglers trolling at or near the
surface, but some anglers target lake
trout by fishing the lower parts of the
water column. A limited number of
subsistence fishing permits are also
issued to tribal members in 1836 Treaty
waters. The magnitude of recreational
harvest varies from year to year and has
averaged 6,600 fish from 1998 to 2002.
From 1998 to 2002, recreational yield of
lake trout averaged 26,200 lb, and in
2002 recreational harvest was 39,700 lb
in MH-2. Starting in 2001, the state of
Michigan raised the minimum size limit
of lake trout in the recreational fishery
from 10” to 20” in areas north of 44° 50’
N latitude. Starting in 2003, the state of
Michigan raised the minimum size limit
of lake trout in the recreational fishery
from 20” to 22” in MH-2. These new
regulations are intended to keep
recreational harvest below the state share
of the MH-2 harvest limit.
213,000 yearling lake trout were planted
annually in Canadian management area
4-3 from 1998 to 2002. After adjusting
for post stocking survival and
immigration and emigration based on
coded-wire-tag data, the MH-2 model
estimates 367,000 yearling lake trout
recruits in MH-2 for 2002.
In contrast to MH-1, there is no
commercial harvest of lake trout in
Michigan waters of MH-2.
As of
August 2000, tribal commercial fishers
may deploy trap nets that target lake
whitefish in 1836 waters of MH-2. This
fishery is not allowed to market lake
trout bycatch.
Two state-licensed
commercial fishing operations (Gauthier
and Spaulding Fisheries, and Rochefort
Fisheries) operate trap nets targeting
lake whitefish in MH-2 south of the 45th
parallel. These operations are also not
allowed to market lake trout bycatch.
All lake trout are returned to the water,
regardless of condition. Prior to the
signing of the Consent Decree, both
state-licensed fisheries operated trap nets
north of North Point. These fisheries
were moved south of the 45th parallel to
accommodate the new tribal trap-net
operations as stipulated in the Consent
Decree.
There is a substantial commercial
fishery for lake trout in Canadian waters
adjacent to MH-2 (areas 4-2, 4-3, and 47) that we included in our assessment.
From 1998 to 2002, total Canadian
commercial lake trout yield in these
areas averaged 44,600 lb per year. The
majority of this yield came from the
large-mesh gill-net fishery. Canadian
large-mesh gill-net effort averaged 6.5
million ft per year from 1998 to 2002.
The state-licensed recreational
fishery in MH-2 is composed of both
charter and non-charter anglers. Lake
trout are frequently caught as bycatch by
Recreational fishery lake trout harvest
14,000
12,000
*No creel data available 1989-90.
10,000
8,000
6,000
4,000
2,000
0
1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
In most years, the dominant
source of mortality for lake trout in MH2 was sea lamprey.
Sea lampreyinduced mortality was greater than all
other mortality sources from 1984 to
1999 with the exception of 1986, 1987,
1990, 1995, and 1996 when natural
mortality was the largest single mortality
source. Sea lamprey mortality rates
have been cyclic in north-central Lake
Huron, reaching peaks in 1989, 1994,
1997, and 1999. From 1998 to 2002, sea
lamprey-induced mortality averaged
39
0.19 y-1, and sea lamprey-induced
mortality rates have been declining
drastically since 1999. Sea lampreyinduced mortality rates for age 6-11 lake
trout in 2002 decreased 87% from the
average of 1994-1998 levels.
This
decline is likely due to the treatment of
the St. Marys River. Recreational and
commercial fishing mortality were low
in most years relative to lampreyinduced mortality; however, increases in
commercial harvest of lake trout in
Canadian waters have caused the
commercial fishing mortality rate to
increase substantially since 1999.
Lake trout biomass and SSB in MH-2
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Year
The Modeling Subcommittee of
the TFC recommends a lake trout
harvest limit of 82,100 lb for MH-2 in
2003. This harvest was calculated using
the target total annual mortality rate of
40% and allocating 95% of the harvest
to the state and 5% of the harvest to the
tribes as outlined in Sections VII.A.3
and VII.A.4 of the Consent Decree.
Based on these calculations, the total
yield was allocated 78,600 lb to the state
and 3,500 lb to the tribes. Due to state
overharvest in MH-2 in 2002, the TFC
applied penalty provisions outlined in
Sections VII.B.4.a and VII.B.4.b of the
Consent Decree and re-allocated the
2003 harvest limits as follows: 61,000
lb to the state and 21,100 lb to the
tribes.
Current spawning stock biomass
per recruit (SSBR) is above SSBR at
target mortality, indicating total annual
mortality rates are below the target of
40% total annual mortality. This is due
to the large declines in sea lampreyinduced mortality rates in 2000, 2001,
and 2002.
If sea lamprey-induced
mortality remains low, spawning stock
biomass and SSBR should increase.
State harvest was significantly
higher than the state harvest limit in
2002. No tribal harvest was reported in
MH-2 in 2002. All tribal fishers in MH2 fish trap nets and are required to
release all lake trout regardless of
condition.
Instantaneous mortality rates (age 6-11)
0.8
Recreational
Commercial
Lamprey
Natural
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1984
1986
1988
1990
1992
1994
1996
1998
2000
Total Biomass
SSB
2002
Year
The high rate of lamprey-induced
mortality in most years caused the age
structure in north-central Lake Huron to
be truncated just before the age of first
maturity. As a result, spawning stock
biomass is low in north-central Lake
Huron. Total lake trout biomass has
steadily increased since 1984, averaging
1,533,700 lb from 1998 to 2002;
however, the majority of this biomass is
young, immature, hatchery fish. From
1998-2002, spawning stock biomass
(SSB) averaged only 148,700 lb in MH2.
40
The total harvest limit increased
significantly from 2002 to 2003. This is
due to the large declines in sea lampreyinduced mortality rates from 2000-2002.
Section VII.A.6 of the Consent Decree
states that for fully phased in units
“changes in harvest limits from year to
year shall not result in adjustments
greater than a fifteen percent (15%)
increase or decrease from the previous
year in that unit, unless all parties agree
that a greater change is appropriate.”
For MH-2 in 2003 all parties agreed that
increasing the harvest limit by greater
than the 15% threshold was appropriate.
Yearly harvest and harvest limits
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
Tribal Harvest
State Harvest
Harvest Limit
2001
2002
Year
2003
41
Summary Status MH-2 Lake Trout
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
1.99 lb
4y
6.04 lb
7y
Spawning biomass per recruit
Base SSBR
2.572 lb
(SE 0.385)
0.85 lb
(SE 0.16)
0.646 lb
(SE 0.051)
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
0.331
(SE 0.022)
Average yield per recruit
0.265 lb
(SE 0.026)
Natural Mortality (M)
0.262 y
Fishing Mortality
Age of full selection
Commercial Fishery (2000-2002)
Age of full selection
Sport fishery (2000-2002)
Commercial Fishing mortality (F)
(average 2000-2002, ages 6-11)
-1
6
6
-1
0.052 y
(SE 0.011)
Sport fishery F
(average 2000-2002, ages 6-11)
-1
0.017 y
(SE 0.003)
Sea lamprey mortality (ML)
(average ages 6-11,2000-2002)
0.094 y
-1
Total mortality (Z)
(average ages 6-11,2000-2002)
Recruitment (age-1)
(1993-2002 average)
-1
0.425 y
(SE 0.023)
411,280 fish
(SE 22,271)
Biomass (age 3+)
(1993-2002 average)
1,506,500 lb
(SE 136,180)
Spawning biomass
(1993-2002 average)
122,810 lb
(SE 17,692)
MSC recommended yield limit for 2003
Actual yield limit for 2003
42
82,100 lb
82,100 lb
Lake Michigan
MM-123 (Northern Lake Michigan)
Prepared by Jory L. Jonas, John Netto, Erik J. Olsen, Steve Lenart, and Mark Ebener
Commercial fishing is also restricted in
the innermost area of Little Traverse Bay
(grid 519) and portions of grid 306 in
northern Green Bay.
Recruitment of lake trout in the
northern management unit of Lake
Michigan is currently based entirely on
stocking. In each of the last ten years,
approximately 682,000 yearling lake
trout have been stocked into northern
Lake Michigan and approximately 87
percent of these fish are stocked into the
northern refuge area.
To more
accurately estimate recruitment in the
model, the number of fish stocked is
adjusted to account for mortality and
movement among the various regions in
the lake. Over the last 10 years (19932002) the recruitment to age one has
averaged 531,500 fish in northern Lake
Michigan.
Both state and tribal commercial
fisheries operate in northern Lake
Michigan. State-licensed commercial
fisheries
are
primarily
trap-net
operations targeting lake whitefish and
are not permitted to harvest lake trout.
Therefore this harvest is considered in
lake trout harvest allocations. While the
current tribal commercial fishery
primarily targets lake whitefish, lake
trout are sometimes targeted or kept as
by-catch.
Since 1981 commercial
fishing has killed more harvestable lake
trout (fish > 17 in.) than other sources of
mortality in northern Lake Michigan
(Figure 1).
Lake trout management unit
MM-123 is made up of statistical
districts MM-1, MM-2 and MM-3 and
encompasses Michigan’s waters of
northern Lake Michigan and northern
Green Bay.
This management unit
covers 5,000 square miles. Water depths
in more northern waters are for the most
part less than 150 feet, and
approximately 3,800 square miles (twothirds of the area) are less than 240 feet.
In southern portions of the unit, depths
can be greater than 550 feet. Most of the
historically important
lake
trout
spawning reefs in Lake Michigan are
located in MM-123. The unit also
contains many islands including the
Beaver Island complex (Beaver, Hat,
Garden, Whiskey, Trout, High and
Squaw Islands), North and South Fox
Islands, and Gull Island in Lake
Michigan. Another series of islands
form a line separating Green Bay from
Lake Michigan; these include Little
Gull, Gravely, St. Martins, Summer and
Poverty Islands. This management unit
is entirely in 1836 Treaty waters, and
contains a lake trout refuge.
The
northern refuge is nearly 900 square
miles and occupies the southern ½ of
grids 313 and 314, grids 413, 414, 513516, the northwest quarter of grid 517,
grid 613, and the northern ½ of grid 614.
It is illegal for recreational fishers to
retain lake trout when fishing in the
refuge.
Gill-net fishing (both
commercial and subsistence) is also
prohibited.
Commercial trap-net
operations are permitted; however, the
retention of lake trout is not allowed.
43
predation (Figure 2). In 1991, the
minimum size limit for sport fishing in
the northern management unit of Lake
Michigan was increased from 10 to 24
inches, a modest decline in recreational
yield resulted. In recent years, the
estimated recreational yield of lake trout
has declined further, by over 89 percent
from 1998 (67,000 lb) to 2002 (7,000
lb). The numbers harvested declined
similarly, 44 percent fewer fish were
harvested in 2002 (Figure 1). More
recent declines are due in part to
declines in recreational fishing effort, as
angler hours decreased nearly 72
percent, from 87,000 in 1998 to 25,000
in 2002.
Figure 1. Number of lake trout killed by source in MM-123
250
200
Commercial
Recreational
Sea Lamprey
150
100
50
0
Year
There are three types of tribal
commercial fisheries, large-mesh gill
net, small-mesh gill net, and trap net.
The large-mesh gill-net fishery accounts
for the majority of the yield. Predicted
tribal commercial yield increased from
370,000 lb in 1991 to 840,000 lb in
1998. After the implementation of the
2000 Consent Decree, yield fell to
591,000 lb in 2001 and 320,000 lb in
2002. Large-mesh gill-net effort in
tribal fisheries has been steadily
declining from 23 million feet in 1992
and 1993 to 5 million feet in 2002. The
number of lake trout harvested in
northern Lake Michigan tribal fisheries
had increased from 1991 (62,000 fish)
until 1998 (144,000 fish). More recently
harvest numbers have declined to 65,000
fish in the year 2002 (Figure 1). Lake
trout harvest in the region is not likely to
experience further declines until 2006
when harvest requirements are fully
phased in as part of the established 2000
Consent Decree.
Figure 2. Instantaneous mortality rates for lake trout ages 6-11 in MM-123
1
Natural
Commercial
Recreational
Sea Lamprey
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
0
Year
Since 1989 sea lamprey-induced
mortality has been the second highest
source of mortality for lake trout in
northern Lake Michigan. During the
recent six years (1997 to 2002) lamprey
mortality rates have been higher than
during the previous sixteen years (Figure
2). The number of lake trout killed by
sea lamprey has increased from an
average of 4,000 fish per year during
1981-1989 to over 38,000 fish per year
during 1997-2002 (Figure 1).
In northern Lake Michigan, lake
trout generally are both spawning and
recruited
into
commercial
and
recreational fisheries by age 7 (Summary
table). The biomass of lake trout in
northern Lake Michigan had nearly
The management of recreational
fisheries for lake trout is the primary
responsibility of the state of Michigan
and fisheries are comprised of both
charter and sport anglers. The mortality
rate of lake trout resulting from
recreational fishing in the northern
management unit of Lake Michigan is
significantly lower than rates associated
with commercial fishing or sea lamprey
44
tripled from 1986 to 1997 increasing
from 1.5 to 4.3 million pounds. Since
1997, the biomass of lake trout has
steadily decreased. In 2002 levels were
almost half those observed in 1997 (2.1
million pounds; Figure 3). The total
biomass of lake trout outside the refuge
has averaged 2.9 million lb during the
last five years (1998-2002). Spawning
biomass showed similar patterns in
abundance with a less pronounced peak
in 1997. Declines in biomass since 1997
are more pronounced when only
considering fish outside the refuge.
The spawning stock biomass
produced per recruit (including the
refuge population) during 2002 is similar
to the target value indicating that
mortality rates for the combined
refuge/non-refuge population are near
the 40% mortality target for this area.
The recommended yield limit for
1836 Treaty waters in 2002 is 28,700
pounds for the state recreational fishery
and 453,000 pounds for the tribal
commercial/subsistence fishery. These
values reflect phase-in requirements
specified in the 2000 Consent Decree.
When fully phased in, yield allocations
in this management unit will allot 10%
to the state of Michigan and a 90% to
tribal fisheries, while meeting the 40%
mortality target. In 2002, two options
were considered: 1) the modeled
allowable yield (259,000 lbs tribal); or
2) the average of the yield from 19971999 less the reduction due to gill-net
conversions in the area (453,000 lbs
tribal). Consistent with the Consent
Decree specifications, option two was
selected and approved by the TFC
because it provided the highest tribal
yield of lake trout. This specific phasein option actually allows a temporary
increase in mortality rates above the
40% target (Figure 4).
Figure 3. Estimated lake trout biomass in MM-123
4500
Total
Spawning Stock
4000
3500
3000
2500
2000
1500
1000
500
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
F ig u re 4 . C o m p a ris o n o f a c tu a l h a rv e s t v s . T A C d e c is io n
v s . m o d e l re c o m e n d a tio n
Lake trout harvested (pounds)
800000
R e c re a tio n a l H arv e s t
C o m m e rc ia l H a rv e st
R e c re a tio n a l T A C
C o m m e rc ia l T A C
M o d e l re c re a tio n a l T A C
M o d e l c o m m e rc ial T A C
600000
400000
200000
0
1998
1999
2000
2001
Year
45
2002
2003
Summary Status MM-123
Female maturity
Size at first spawning
Age at first spawning
Size at 50% maturity
Age at 50% maturity
Value (95% probability interval)
1.51 lb
3y
6.50 lb
6y
Spawning stock biomass per recruit
Base SSBR
Current SSBR combined w/ refuge
SSBR at target mortality
7.196 lb (6.079 – 8.244)
1.94 lb (0.93 – 1.75)
2.145 lb (1.866 – 2.431)
Spawning potential reduction
At target mortality
0.298 (0.268 – 0.337)
Average yield per recruit
1.280 lb (1.166 – 1.400)
0.236 y-1
Natural mortality (M)
Fishing mortality
Age of full selection
Commercial fishery (2000-2002)
Sport fishery (2000-2002)
Commercial fishing mortality (F)
Average 2000-2002, ages 6-11
Sport fishing mortality (F)
Average 2000-2002, ages 6-11
7y
7y
0.377 y-1 (0.293 – 0.506)
0.01 y-1 (0.008 – 0.015)
Sea lamprey mortality (ML)
Average 2000-2002, ages 6-11
0.178 y-1
Total mortality (Z)
Average 2000-2002, ages 6-11
0.801 y-1 (0.717 – 0.935)
Recruitment (age-1)
Average 1993-2002
531,460 fish (421,654 – 708,500)
Biomass (age 3+)
Average 1993-2002
3,309,700 lb (2,831,840 - 3,738,790)
Spawning biomass
Average 1993-2002
568,350 lb (456,295 – 647,133)
MSC recommended yield limit for 2003 (modelgenerated)
Actual yield limit for 2003 (phase-in requirements)
46
287,700 lb
481,700 lb
MM-4 (Grand Traverse Bay)
Prepared by Jory L. Jonas, John Netto, and Erik J. Olsen
Lake Michigan. In each of the last ten
years, on average, 255,000 yearling lake
trout have been stocked into Grand
Traverse Bay.
To more accurately
estimate recruitment in the model, the
number of fish stocked is adjusted to
account for variations in mortality and
movement among the various regions in
the lake. Over the last 10 years (19932002) the recruitment to age one has
averaged 227,000 fish in the Grand
Traverse management unit (Summary
table).
From 1993 until 1998 more lake
trout were killed by commercial fishing
than by either sea lamprey or sport
fishing (Figure 1). However, during
1999-2002 the numbers killed by the
three mortality sources were more
similar and lamprey wounding had
increased. Commercial fishing mortality
in Grand Traverse Bay peaked in 1994 at
0.56 y-1, remained stable over the next
six years averaging of 0.24 y-1, and in
the recent few years has declined to a
level of 0.12 y-1 in 2002 (Figure 2).
Lake trout management unit
MM-4 encompasses the Grand Traverse
Bay region of Lake Michigan, and is
also called the MM-4 statistical district.
There are two islands in this
management unit, Bellow and Marion
Island. A large peninsula bisects the
southern half of the bay. For the most
part water depths in the bay range up to
280 feet. However, waters on either side
of the peninsula are much deeper,
ranging to 440 feet in the west arm and
640 feet in the east arm.
This
management unit is entirely in 1836
Treaty waters. There are no refuge areas
allocated, however commercial fishing is
prohibited in the southern most portion
of the bay (grids 915 and 916). The total
area of the unit is 255 square miles of
which 168 square miles are less than 240
feet in depth. Based on estimates from
historical commercial catch rates only a
small amount of lake trout spawning
habitat is located in the management
unit. However, Grand Traverse Bay is
one of the only areas of Lake Michigan
where the recruitment of naturally
reproduced lake trout has been
documented. In the mid-1980’s the
frequency of unclipped fish in the bay
increased significantly leading biologists
to believe that rehabilitation efforts were
succeeding.
Unfortunately, in more
recent evaluations few unclipped lake
trout have been seen.
This area
constitutes an area of high use by both
tribal and state interests.
The recruitment of lake trout in
Grand Traverse Bay is based entirely on
stocking. The U.S Fish and Wildlife
Service is the primary agency
responsible for stocking lake trout in
Figure 1. Number of lake trout killed by source in MM-4
60
50
40
Commercial
Recreational
Sea Lamprey
30
20
10
0
Year
Only
tribal
fishermen
commercially harvest fish in this
management unit. There are three types
of tribal commercial fisheries, largemesh gill net, small-mesh gill net, and
trap net. The large-mesh gill-net fishery
47
24 inches. In 1996 the season for
harvesting lake trout was lengthened, so
that it extended from Jan 1 through
September 30 in contrast to the previous
season of May 1 through Labor Day.
Mid-way through the year in 1997 the
minimum size limit was decreased to 20
inches and has remained so through
2002. The mortality rates of lake trout
resulting from recreational fishing
steadily declined from 1991 (0.26 y-1) to
1996 (0.08 y-1). Increases in recreational
fishing mortality were observed in 1998
to 0.26 y-1 in response to reductions in
the size regulations. Despite lower size
regulations, mortality has declined
averaging 0.26 y-1 during the recent
three years (2000-2002; Figure 2). The
estimated recreational yield of lake trout
in Grand Traverse Bay had been
consistent during the years 1992-1996
averaging 39,000 lb. In response to
changes in size regulations from 1996 to
1998 the recreational yield of lake trout
increased dramatically to 93,000 lb. In
recent years (2001-2002) yield has
declined, falling to 35,000 lb. The
numbers of lake trout harvested followed
similar patterns to that observed for
yield. Harvest remained stable from
1992 through 1996 averaging 6 thousand
fish.
Harvest
then
increased
dramatically peaking at 19 thousand fish
in 1998. More recently, the harvest of
lake trout has declined, falling to 5
thousand fish in 2001 and 2002 (Figure
1). Recreational fishing effort levels
have remained relatively stable over the
last 10 years (1993-2002) averaging 202
thousand angler hours (range=180-240
thousand angler hours).
From 1981-1988 sea lampreyinduced mortality was the lowest source
of mortality in the Grand Traverse Bay
management unit with instantaneous
rates averaging 0.02 y-1. Rates gradually
while primarily targeting lake whitefish
is responsible for the greatest number of
harvested lake trout. The commercial
harvest of lake trout in tribal large-mesh
gill-net fisheries rose from a low of 6
thousand fish in 1991 to 33 thousand
fish harvested in 1998. In recent years,
harvest has been declining, and an
estimated 7 thousand fish were harvested
in 2002. The yield of lake trout captured
in tribal commercial fisheries peaked in
1998 at 135,000 lb and has declined by
nearly 80% to 31,000 lb in 2002. Largemesh gill-net effort in tribal fisheries has
also been declining from 2 million feet
in 1996 to an average of 0.75 million
feet during the last two years (2001 and
2002).
It is expected that major
decreases in the commercial harvest of
lake trout in the Grand Traverse Bay
management unit will be sustained in
future years as a result of converting the
regions largest gill-net fishers to trap-net
operations.
Figure 2. Instantaneous mortality rates for lake trout ages 6-11 in MM-4
1.2
1
0.8
Natural
Commercial
Recreational
Sea Lamprey
0.6
0.4
0.2
0
Year
The management of recreational
fisheries for lake trout is the primary
responsibility of the state of Michigan
and fisheries are comprised of both
charter and sport anglers.
The
sportfishing harvest regulations in the
Grand Traverse Bay management unit
have changed significantly over the last
10 years, affecting recreational fishing
mortality rates and harvest levels. From
1992-1996 the minimum size limit for
lake trout harvest increased from 10 to
48
increased to 0.13 y-1 by 1991, and
declined to 0.05 y-1 in 1994. After 1994
rates were variable and generally
increasing.
The highest lamprey
mortality rate was observed in 1999 at
In 1999, lampreys were
0.21 y-1.
estimated to have killed over 20,000 lake
trout from the management unit. From
1999-2001, mortality rates from sea
lamprey remained high averaging 0.18 y1
. The results of increased lamprey
control efforts were potentially realized
in 2002 as reported mortality rates were
significantly lower at 0.09 y-1. Lamprey
killed approximately 5,000 lake trout in
2002 significantly fewer than had
previously been observed.
In the Grand Traverse Bay
management unit, lake trout are recruited
into commercial fisheries by age 6 and
recreational fisheries by age 7. Female
lake trout in this management unit first
spawn at age 3 and 50 percent or more
are spawning by age 6. The total
biomass of lake trout has averaged
925,000 pounds during the last 10 years
(1993-2002). Lake trout biomass rose
from a low of 0.9 million lb in 1991 to a
high of 1.5 million pounds in 1997.
After the peak in 1997, lake trout
biomass declined to 953,000 lb by 2001.
In 2002 the biomass of age 3 and older
fish appears to be rising at
approximately 1.0 million lb. In 1997, it
was estimated that the spawning stock
biomass was 200,000 lb by the year
2002 the estimate had decreased to
103,000 lb. The biomass of spawning
lake trout in the management unit has
averaged 136,000 lb during the last ten
years (1993-2002).
The spawning stock biomass
produced per recruit is below the target
value indicating that the mortality rate is
too high in Grand Traverse Bay. The
recommended harvest limit for the year
2003 in the Grand Traverse Bay
management unit is 106,100 pounds of
which 46,100 pounds was allocated to
the state recreational fishery and 60,000
pounds
to
the
tribal
commercial/subsistence fishery.
Figure 3. Estimated lake trout biomass in MM-4
1600
Total
Spawning Stock
1400
1200
1000
800
600
400
200
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Grand Traverse Bay represents
an area where unique phase-in
requirements defined in the 2000
Consent Decree were considered in
establishing yield limits (Figure 4).
From 2001 to 2005 commercial limits
are to be set in Grand Traverse Bay
based on mean yield and effort values
from 1997-1999 minus the conversion of
gill-net effort to trap nets. Recreational
yield limits are set at the mean for the
previous three years and are to be
adjusted for regulation changes. From
2006 to 2009 yield and effort limits will
be set to meet the target mortality rate
for this area of 45%, with a 40 percent
allocation to the state of Michigan and a
60 percent allocation to tribal fisheries.
After this allocations will be set at 45
percent to the state and 55 percent to
tribal fisheries.
Figure 4. Com parison of actual harvest vs. TAC decision
vs. m odel recom endation
Lkae trout harvested (pounds)
160000
Recreational harvest
Comm ercial harvest
140000
Recreational TAC
Comm ercial TAC
Mo del recreational TAC
Mo del com mercial TAC
120000
100000
80000
60000
40000
20000
0
1998
1999
2000
2001
YEAR
49
2002
2003
Summary Status MM-4
Female maturity
Size at first spawning
Age at first spawning
Size at 50% maturity
Age at 50% maturity
Value (95% probability interval)
1.51 lb
3y
6.50 lb
6y
Spawning stock biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
2.952 lb (2.587 – 3.374)
0.670 lb (0.579 – 0.776)
0.850 lb (0.780 – 0.926)
Spawning potential reduction
At target mortality
0.226 (0.256 – 0.323)
Average yield per recruit
0.599 lb (0.542 – 0.660)
0.277 y-1
Natural mortality (M)
Fishing mortality
Age of full selection
Commercial fishery (2000-2002)
Sport fishery (2000-2002)
Commercial fishing mortality (F)
Average 2000-2002, ages 6-11
Sport fishing mortality (F)
Average 2000-2002, ages 6-11
7y
7y
0.187 y-1 (0.149 – 0.233)
0.135 y-1 (0.105 – 0.159)
Sea lamprey mortality (ML)
Average 2000-2002, ages 6-11
0.141 y-1
Total mortality (Z)
Average 2000-2002, ages 6-11
0.744 y-1 (0.680 – 0.806)
Recruitment (age-1)
Average 1993-2002
227,000 fish (208,000 – 249,000)
Biomass (age 3+)
Average 1993-2002
925,000 lb (847,000 – 1,030,000)
Spawning biomass
Average 1993-2002
136,000 lb (123,000 – 157,000)
MSC recommended yield limit for 2003 (modelgenerated)
Actual yield limit for 2003 (phase-in requirements)
50
80,000 lb
106,100 lb
MM-5 (Leelanau Peninsula to Arcadia)
Prepared by Jory L. Jonas, John Netto, and Erik J. Olsen
10 years (1993-2002) the recruitment to
age one has averaged 237,000 fish in
MM-5.
Lake trout management unit
MM-5 is located in eastern central Lake
Michigan and corresponds to the MM-5
statistical district. This area constitutes
an area of high use by both tribal and
state interests. The unit covers 2,100
square
miles
and
encompasses
Michigan’s waters of Lake Michigan
from Arcadia north to the tip of the
Leelanau Peninsula, extending to the
state line bisecting the middle of the
lake. There are two islands in this
management unit, the North and South
Manitou Islands. Some of the deepest
waters and largest drop-offs in Lake
Michigan occur in MM-5. Water depths
range to 825 feet and for the most part
are greater than 400 feet. Only 440
square miles of the unit are at depths less
than 240 feet. The entire area is in 1836
Treaty waters and there are no refuges
allocated within the management unit.
Only a small amount of lake trout
spawning habitat is located here, most of
which is located in the near shore zone
and around the North and South Manitou
Islands.
The recruitment of harvestable
lake trout in the MM-5 management unit
of Lake Michigan is based entirely on
stocking. The U.S. Fish and Wildlife
Service is the primary agency
responsible for stocking lake trout in
Lake Michigan. Over the last ten years,
on average, 240,000 yearling lake trout
were
stocked
into
the
MM-5
management unit annually. To more
accurately estimate recruitment in the
model, the number of fish stocked is
adjusted to account for variations in
mortality and for movement among the
various regions in the lake. Over the last
Figure 1. Number of lake trout killed by source in MM-5
60
Commercial
Recreational
Sea Lamprey
50
40
30
20
10
0
Year
Although both state and tribal
commercial fishermen harvest fish in the
management
unit,
state-licensed
commercial fisheries are primarily trapnet operations targeting lake whitefish.
State-licensed fishermen are not
permitted to harvest lake trout, and as a
result, are not included in lake trout
harvest allocations. There are three
types of tribal commercial fisheries,
large-mesh gill net, small-mesh gill net,
and trap net. The large-mesh gill-net
fishery while primarily targeting lake
whitefish, has been responsible for the
greatest number of harvested lake trout
in commercial fisheries.
With the
conversion of the regions largest gill-net
fishers to trap-net operations and
because lake trout were of low market
value; the commercial harvest and
mortality of lake trout have decreased
considerably in recent years. From 1990
to 1993, mortality from commercial
fishing was extremely low, averaging
0.003 y-1. Mortality rates increased over
the next seven years, the highest
commercial fishing mortalities were
observed in 1999 and 2000 at 0.27 and
0.20 y-1, respectively. In 1999 over
51
harvest levels were likely reflecting
declines in the abundance of lake trout.
Between the years 2001 and 2002 angler
hours declined to 236 thousand in
response to poor catch rates and
increases in size regulations.
The
sportfishing harvest regulations in the
MM-5 management unit of Lake
Michigan have historically allowed for
the take of 10-inch lake trout. In 2001
the minimum harvest limit was changed
to 22 inches. As a result, a reduction in
recreational harvest in the MM-5
management unit of Lake Michigan
should continue to be realized in future
years.
25,000 fish were harvested in
commercial
fisheries.
Since
implementing the 2000 Consent Decree,
reductions in mortalities have been
realized. Only around 2,000 lake trout
were harvested each year in 2001 and
2002 and mortality rates averaged 0.02
The tribal
y-1 (Figures 1 and 2).
commercial yield of lake trout rose
precipitously from 0 lb in 1993 to
154,000 lb in 1999. In recent years yield
has declined to near former lows
averaging 6,500 lb. Large-mesh gill-net
effort in tribal fisheries reflected similar
patterns to those observed for mortality,
harvest and yield after 1993. Effort rose
from 0 to 2 million feet in 1999 and by
2002 effort was down to 70 thousand
feet of net.
The recreational fisheries for lake
trout are comprised of both charter and
sport anglers. From 1983 until the late
1990’s, recreational fishing was the
highest source of mortality in the MM-5
management unit, exceeding both sea
lamprey and commercial fishing
mortality. In recent years however,
recreational fishing mortality rates on
lake trout (averaged over ages 6-11)
have dropped significantly from the high
level of 0.21 y-1 observed in 1995 to a
low of 0.06 y-1 in 2002. The yield of
lake trout in recreational fisheries
averaged 82,000 lb over the 13-year
period between 1985 and 1998. In
recent years recreational yield has
declined from 89,000 lb in 1998 to
21,000 lb in 2002. The number of lake
trout harvested in recreational fisheries
have also declined in recent years,
dropping by over 85 percent from 1998
(17,000 fish) to 2002 (3,000 fish).
Recreational fishing effort had been
relatively constant for seven years
(1995-2001) averaging 300 thousand
angler hours, an indication that low
Figure 2. Instantaneous mortality rates for lake trout ages 6-11 in MM-5
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Natural
Commercial
Recreational
Sea Lamprey
Year
From 1981 to 1988 sea lamprey
mortality was less than either
recreational or commercial mortality.
From 1996 to 2000 sea lamprey
mortality rates increased substantially in
the MM-5 management unit. It appears
that sea lamprey induced mortality is
decreasing in recent years (2001 and
2002). Mortality rates have fallen from
a high of 0.21 y-1 in 1999 to 0.08 in 2002
(Figure 2). Sea lamprey killed over
20,000 lake trout in 1999 and 5,000 in
2002. During the last 13 years (1990 to
2002), lampreys have killed an average
of 6,800 lake trout y-1. Prior to 1990
lamprey were only responsible for
killing 1,500 lake trout y-1. The U.S.
Fish and Wildlife Service has initiated
efforts to improve controls on lamprey
populations in northern Lake Michigan.
52
estimated based on a target mortality rate
of 45%. Of this yield, 69,100 pounds
were allocated to the state recreational
fishery and 38,700 pounds to the tribal
commercial and subsistence fisheries.
Allocations were based on a 60 percent
allotment for the state of Michigan and
40 percent to tribal fisheries. Language
in the negotiated 2000 Consent Decree
states that fisheries TAC limits will not
vary by more than 15 percent from year
to year.
In 2002, harvest limits
increased and were higher than 15%
different from the previous year, an
indication that lake trout populations
were improving. As a result, the 15
percent rule was not invoked.
In general, 50 percent of lake
trout in MM-5 are spawning by age 6
and recruited into commercial fisheries
by age 7 and recreational fisheries by
age 9. The total biomass rose to a peak
in 1988, declined, in the late 1980s and
early 1990s and then rose to a high value
in 1997, before declining to levels below
1 million pounds in 2001 and 2002
(Figure 3). The biomass of spawners in
the MM-5 showed similar temporal
patterns with less pronounced peaks.
Figure 3. Estimated lake trout biomass in MM-5
1400
Total
Spawning Stock
1200
1000
800
600
Figure 4. Com parison of actual harvest vs. TAC decision
vs. m odel recom endation
400
200
180000
Lake trout harvested (pounds)
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
The spawning stock biomass
produced per recruit has improved in this
region and is now more similar to and
slightly above the target value, an
indication that mortality is being
controlled in MM-5. The recommended
yield limit for the year 2003 in Unit
MM-5 is 107,800 pounds, which was
Recreational harvest
Com mercial harvest
160000
Recreational TAC
Com mercial TAC
M odel recreational TAC
M odel com mercial TAC
140000
120000
100000
80000
60000
40000
20000
0
1998
1999
2000
2001
Year
53
2002
2003
Summary Status MM-5
Female maturity
Size at first spawning
Age at first spawning
Size at 50% maturity
Age at 50% maturity
Value (95% probability interval)
1.51 lb
3y
6.50 lb
6y
Spawning stock biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
1.974 lb (1.647 – 2.257)
0.790 lb (0.598 – 0.991)
0.636 lb (0.559 – 0.722)
Spawning potential reduction
At target mortality
0.322 (0.301 – 0.360)
Average yield per recruit
0.347 lb (0.293 – 0.397)
0.298 y-1
Natural mortality (M)
Fishing mortality
Age of full selection
Commercial fishery (2000-2002)
Sport fishery (2000-2002)
Commercial fishing mortality (F)
Average 2000-2002, ages 6-11
Sport fishing mortality (F)
Average 2000-2002, ages 6-11
7y
9y
0.085 y-1 (0.060 – 0.119)
0.085 y-1 (0.061 – 0.121)
Sea lamprey mortality (ML)
Average 2000-2002, ages 6-11
0.100 y-1
Total mortality (Z)
Average 2000-2002, ages 6-11
0.548 y-1 (0.507 – 0.613)
Recruitment (age-1)
Average 1993-2002
237,000 fish (218,000 – 270,000)
Biomass (age 3+)
Average 1993-2002
839,000 lb (721,000 – 993,000)
Spawning biomass
Average 1993-2002
143,000 lb (115,000 – 173,000)
MSC recommended yield limit for 2003
Actual yield limit for 2003
107,800 lb
107,800 lb
54
MM-67 (Manistee - Ludington)
Prepared by Jory L. Jonas, John Netto, and Archie W. Martell Jr.
Lake trout management unit MM67 is located in eastern central Lake
Michigan, and is made up of statistical
districts MM-6 and MM-7. The area
covers Michigan’s waters of Lake
Michigan from Arcadia to Holland,
extending to the state line bisecting the
middle of the lake. The management unit
covers a total area of 4,460 square miles, of
which 930 square miles are less than 240
feet in depth. The northern section of the
region (MM-6) is deeper ranging in depth
from 0 up to 900 feet and is characterized
by greater slope than the southern section
(MM-7). For the most part water depths in
MM-7 are less than 400 feet. There are no
islands or structures in southern treaty
waters, and there is little lake trout
spawning habitat with the exception of
offshore deepwater spawning reefs located
within the mid-lake refuge. Stocked lake
trout almost certainly attempt to spawn in
the nearshore zones.
However, the
likelihood of successful recruitment is
negligible.
The
southern
treaty
management unit is not entirely comprised
of 1836-treaty waters, the northern section
(MM-6) is entirely treaty ceded territory
while only the northern two-thirds of the
southern section (MM-7) is within treaty
territory. A total of 690 square miles in the
unit are outside treaty waters. A line
running parallel to the northern side of the
Grand River (located approximately ¾ of
the way through grids in the 1900 series)
out to the state line in the middle of the lake
delineates the southern boundary of treaty
territories in the unit. Management unit
MM-67 contains a portion of the deepwater
mid-lake lake trout refuge, which
comprises 850 square miles of the unit
(grids 1606, 1607, 1706, 1707, 1806, 1807,
55
1906 and 1907).
It is illegal for
recreational fishers to retain lake trout
when fishing in the refuge area. Gill-net
fishing (both commercial and subsistence)
are prohibited in the refuge, some state
and tribal licensed commercial trap-net
operations are permitted, however, the
retention of lake trout is prohibited. As of
the year 2002 there was no tribal
commercial fishing effort in management
unit MM-7 and limited tribal fishing
existed in MM-6.
The recruitment of lake trout in the
southern treaty waters of Lake Michigan is
based entirely on stocking. During the
past ten years, an average of 192,000
yearling lake trout have been stocked into
non-refuge southern treaty waters, while
an additional 319,000 fish were stocked
into the mid-lake refuge area much of
which is in Wisconsin’ waters. To more
accurately estimate recruitment in the
model, the number of fish stocked is
adjusted to account for varying mortality
and for movement among the various
regions in the lake. Over the last 10 years
(1993-2002) the recruitment of lake trout
to age one has averaged 378,000 fish in
the southern treaty management unit of
Lake Michigan.
Since 1986 commercial fishing has
killed many fewer lake trout of harvestable
size in the southern unit (MM-67) than
either recreational fishing or sea lamprey
(Figure 1).
In the year 2002, the
commercial fishery in southern treaty
waters of Lake Michigan was comprised
of only a few state-licensed commercial
fishers and one tribal trap-net operation.
State and tribal licensed commercial
fisheries primarily target lake whitefish
and chubs, and they are not permitted to
2002).
Fluctuations in effort mirror
harvest fluctuations in this management
unit, declining from 1987 to 1999 and
increasing slightly in recent years. The
minimum size limit for lake trout in the
MM67 management unit is 10-inches, the
bag limit is two fish per day, and the
recreational fishing season extends from
January 1 until Labor Day. The size and
bag limits have not changed since 1981.
However, the fishing season has changed
twice, once in 1984 where the season was
restricted from the entire year to May 1
through August 15th, and again in 1989
when the season was extended through
Labor Day.
Sea lamprey-induced mortality is
lower in southern treaty waters of Lake
Michigan, when compared with rates
observed in the northern units. Rates
ranged from 0.007 to 0.12 (Figure 2). In
the last five years (1998-2002), the
number of lake trout killed by lamprey
averaged 23,000 fish (Figure 1).
harvest lake trout. As a result, state and
tribal commercial fishermen are not
included in lake trout harvest allocations.
The yield of lake trout in commercial
fisheries has averaged 2,300 pounds over
the last 17 years (1986-2002) in
management unit MM67. On average
commercial fishers have harvested around
800 fish/year from 1998-2002. As a result
of stipulations of the 2000 consent decree,
this area will experience greater
commercial fishing effort from tribal
interests in the future.
Figure 1. Number of lake trout killed by source in mm-67
100
90
Commercial
Recreational
Sea Lamprey
80
70
60
50
40
30
20
10
0
Year
State recreational fisheries for lake
trout are comprised of both charter and
sport anglers.
In general, recreational
fishing mortality has been higher than
either commercial fishing mortality or
mortality due to sea lamprey (Figure 2).
From 1998 to 1999 observed recreational
fishing mortality rates dropped by nearly 64
percent from 0.11 to 0.02 y-1. By 2002
recreational fisheries had recovered, and
the mortality rate had increased to near
former levels (0.07 y-1). The yield of lake
trout in recreational fisheries peaked in
1987 at 474,000 lb, declined to 113,000 lb
in 1999, rose to 178,000 lb in 2001 and was
down again in 2002 (132,000 lb). The
numbers of lake trout harvested had
declined by nearly 80 percent from 1987 to
1999 with a peak of 81,000 fish in 1987
and a low of 17,000 fish in 1999 (Figure 1).
In recent years the recreational harvest of
lake trout is somewhat higher averaging
25,000 fish in the last three years (2000 to
Figure 2. Instantaneous mortality rates for lake trout ages 6-11 in mm-67
0.6
0.5
Natural
Commercial
Recreational
Sea Lamprey
0.4
0.3
0.2
0.1
0
Year
In general in MM-67 lake trout are
both spawning and recruited into
commercial and recreational fisheries by
age 6. The total biomass of lake trout
averaged over 3 million lb during the
recent ten years (1993-2002; Figure 3).
Spawning lake trout comprise a relatively
high proportion of the total biomass in this
unit (Figure 3), averaging nearly 1.0
million lb from 1993-2002. The spawning
biomass of lake trout in MM-67 followed
56
similar temporal patterns to those observed
for total biomass.
The spawning stock biomass
produced per recruit is significantly above
the target value indicating that target
mortality rates have been achieved in MM67 (Summary table).
The recommended yield limit for
the year 2003 in MM-67 is 471,700 lb. Of
this, 431,400 pounds are allocated to the
state recreational fishery and 40,300
pounds to the tribal fishery. The yield limit
and allocations in this management unit are
set to achieve a total mortality rate target of
40% and establish a 90 percent allocation
to the state of Michigan and a 10 percent
allocation to tribal fisheries.
Both
recreational and commercial fisheries are
well below established TAC levels (Figure
4).
Figure 3. Estimated lake trout biomass in mm-67
4500
Total
Spawning Stock
4000
3500
3000
2500
2000
1500
1000
500
0
1981
1983
1985
1987
1989
1991 1993
Year
1995
1997
1999
2001
Lake trout harvested (pounds)
Figure 4. Comparison of actual harvest vs. TAC decision
800000
Recreational harvest
Commercial harvest
Recreational TAC - fully phased
Commercial TAC - fully phased
600000
400000
200000
0
1998
1999
2000
2001
2002
2003
Year
57
Summary Status MM-67
Female maturity
Size at first spawning
Age at first spawning
Size at 50% maturity
Age at 50% maturity
Value (95% probability interval)
1.34 lb
3y
6.14 lb
6y
Spawning stock biomass per recruit
Base SSBR
Current SSBR combined w/ refuge
SSBR at target mortality
5.800 lb (4.539 – 7.176)
2.390 lb (1.716 – 2.966)
1.272 lb (1.062 – 1.465)
Spawning potential reduction
At target mortality
0.219 (0.191 – 0.253)
Average yield per recruit
0.439 lb (0.396 – 0.487)
0.201 y-1
Natural mortality (M)
Fishing mortality
Age of full selection
Commercial fishery (2000-2002)
Sport fishery (2000-2002)
Commercial fishing mortality (F)
Average 2000-2002, ages 6-11
Sport fishing mortality (F)
Average 2000-2002, ages 6-11
6y
6y
0.003 y-1 (0.002 – 0.004)
0.070 y-1 (0.054 – 0.100)
Sea lamprey mortality (ML)
Average 2000-2002, ages 6-11
0.099 y-1
Total mortality (Z)
Average 2000-2002, ages 6-11
0.373 y-1 (0.344 – 0.414)
Recruitment (age-1)
Average 1993-2002
378,000 fish (357,000 – 404,000)
Biomass (age 3+)
Average 1993-2002
3,081,000 lb (2,295,000 – 3,898,000)
Spawning biomass
Average 1993-2002
919,000 lb (635,000 – 1,220,000)
MSC recommended yield limit for 2003
Actual yield limit for 2003
471,700 lb
471,700 lb
58
STATUS OF LAKE WHITEFISH POPULATIONS
Lake Superior
WFS-04 (Marquette - Big Bay)
Prepared by Philip J. Schneeberger
Lake whitefish unit WFS-04
(1,201,498 surface acres) is located in
Lake Superior roughly between Big Bay
and Laughing Fish Point east of
Marquette. Fishable grids in this unit
include 1326-1327, 1428-1429, and
1529-1531. Near shoreline features of
this zone includes many points, bays,
islands, and in-flowing rivers. Habitat
suitable for lake whitefish growth and
reproduction is associated with many of
these features.
Commercial lake whitefish yield WFS-04
500
450
400
350
300
250
200
150
100
50
0
Trap Net
GillNet
TAC
Year
Fishing effort declined for both
types of commercial gear. Trap-net
effort in 2001 (272 lifts) was lower than
for any year since 1997. Gill-net effort
(420 thousand ft) was 35% above the
1991-99 average but was 33% below the
value for 2000.
This unit historically has been
treated as a single management area
though it certainly contains several
reproductively isolated stocks.
It
contains waters both within and outside
the 1836 Treaty area, but more than 90%
of trap-net effort and yield are taken
from waters west of the treaty line.
Lake whitefish commercial trap net and gill net effort WFS-04
6
Trap Net
Gill Net
5
Yield during 2001 was 73
thousand lbs with 46 thousand lbs (63%)
caught in trap nets and 27 thousand lbs
(37%) in gill nets. Trap-net yield was
low but gill-net yield was slightly higher
compared to averages from 1986
through 2000. On average, trap nets
have caught about three-quarters of the
annual yield from 1986 through 2001.
0.8
0.7
0.6
4
0.5
3
0.4
0.3
2
0.2
1
0.1
0
0
Year
Calculations of mean weight-atage were lower in 2001 than in 2000 for
ages 4-8 and 12+. Values were lower
for all ages in 2001 compared to 19862000 averages.
59
Total instantaneous mortality
rates (Z) have been stable and low over
the last eight years relative to the period
from 1988 through 1993. Estimated
instantaneous fishing mortality rates (F)
were 0.06 y-1 for gill nets and 0.12 y-1
for trap nets in 2001. Instantaneous
natural mortality rate was 0.19 y-1.
Lake whitefish population mean weight at age WFS-04
7
Age-4
Age-6
Age-8
Age-10
6
5
4
3
2
1
0
Instantaneous mortality rates for lake whitefish WFS-04
0.7
Year
0.6
Recruitment (number of age-4
lake whitefish) was estimated at 81,000
in 2001. Estimates of recruitment have
been stable from 1994 through 2001.
0.5
Natural
Trap Net
Gill Net
Sea Lamprey
0.4
0.3
0.2
0.1
Lake whitefish recruitment (age-4)WFS-04
180
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
160
140
The calculated yield limit for
2003 is 200,000 lbs in WFS-04. Yield
limits have decreased each year since
2001. It is a struggle to understand these
decreases since indicators and trends
appear to be generally favorable.
120
100
80
60
40
20
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
A seven-year positive trend
continued in 2001 for estimates of both
fishable biomass and spawning stock
biomass. Estimated fishable biomass
was 748 thousand lbs and spawning
stock biomass was 552 thousand lbs in
2001. The ratio of spawning stock
biomass to fishable biomass was 0.74.
Estimated lake whitefish biomass WFS-04
900
800
700
600
500
400
300
200
Total
Spawning Stock
100
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
60
Summary Status WFS-04 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.85 lb
4y
2.00 lb
5y
7.352 lb
(SE 0.012)
2.46 lb
(SE 0.07)
0.231 lb
(SE 0.000)
0.334
(SE 0.010)
1.376 lb
(SE 0.010)
-1
0.188 y
Natural Mortality (M)
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
9
9
-1
Average gill net F, ages 4+
0.07 y
(SE 0.004)
Average trap net F, ages 4+
0.153 y
(SE 0.007)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.412 y
(SE 0.01)
Recruitment (age-4)
(1992-2001 average)
76,161 fish
(SE 3,882)
Biomass (age 3+)
(1992-2001 average)
591,980 lb
(SE 23,762)
Spawning biomass
(1992-2001 average)
406,830 lb
(SE 17,057)
MSC recommended yield limit for 2003
Actual yield limit for 2003
61
200,000 lb
200,000 lb
WFS-05 (Munising)
Prepared by Philip J. Schneeberger
to 1.27 million ft). From 1996 to 2001,
trap-net
effort
has
fluctuated
considerably but gill-net effort has been
relatively steady. Compared to 19862000 averages, fishing effort during
2001 was lower by 29% for the trap-net
fishery and by 32% for the gill-net
fishery.
The WFS-05 lake whitefish
management extends approximately
from Laughing Point to Au Sable Point
in Lake Superior.
Surface area is
1,845,495 acres. Several bays (Shelter
Bay, Au Train Bay, South Bay, and
Trout Bay) and islands (Au Train Island,
Wood Island, Williams Island, and
Grand Island) are prominent in this area,
providing substrate and depth contours
suitable for lake whitefish habitat and
spawning.
Different whitefish stocks
exist within this unit, including a
smaller, slower-growing stock identified
in Munising (South) Bay.
Lake whitefish commercial trap net and gill net effort WFS-05
600
10
3
2.5
2
6
1.5
4
2
Trap Net
Gill Net
1
0.5
0
0
Year
Mean weight-at-age values were
less in 2001 than in 2000 for ages 4-12+.
These lower values reflect an on-going
decline in whitefish weight-at-age that
has been evident throughout the 19862001 data series.
Lake whitefish population mean weight at age WFS-05
8
Age-4
Age-6
Age-8
Age-10
7
Commercial lake whitefish yield WFS-05
700
3.5
8
Total yield of lake whitefish in
WFS-05 for 2001 was 144 thousand lbs.
This represented a 33% decrease from
the yield in 2000 and a 15% decrease
over the average yield from 1986
through 2000. Trap nets accounted for
55% of the lake whitefish yield during
2001, and gill nets took the remaining
45%. Trap-net yield has varied without
trend since the early 1990s whereas gillnet yield has shown an increasing trend
since 1995.
800
12
6
Trap Net
GillNet
TAC
5
4
3
500
2
400
1
300
0
200
100
Year
0
The
2001
estimate
of
recruitment, measured as annual
estimated numbers of age-4 lake
whitefish in the population, dropped
precipitously from current estimates for
Year
Trap-net effort fell 42% from
2000 (930 lifts) to 2001 (535 lifts), while
gill-net effort went down 6% (from 1.36
62
Natural mortality rate (M) was the
largest component (73%) of Z in WFS05. Instantaneous fishing mortality (F)
rate was 0.03 y-1 for gill nets and 0.06 y-1
for trap nets.
1999 and 2000. Estimated recruitment
in 2001 was 164,000 fish, but prior
experience dictates that this estimate is
subject to revision in subsequent years.
For example, the recruitment estimate in
2000 using the 1986-2000 data set was
155,000, but adding one more year of
data (1986-2001 data set) changed the
2000 estimate to 565,000.
Instantaneous mortality rates for lake whitefish WFS-05
0.6
0.5
Natural
Trap Net
Gill Net
Sea Lamprey
0.4
Lake whitefish recruitment (age-4)WFS-05
0.3
600
500
0.2
400
0.1
300
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
200
The calculated 2003 yield limit
for WFS-05 was 745,000 lbs, a 16%
increase from the yield limit in 2002.
Increased effort and yield from the gillnet fishery would be necessary to reach
the 2003 TAC while maintaining the
mandated split between tribal and statelicensed fishers.
100
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
Biomass estimates in 2001 were
3.02 million lbs for the fishable stock
(lake whitefish age-4 and older) and 2.02
million lbs for the spawning stock.
These values represent declines from
estimates for 2000 and mark the end of
increasing trends for biomass estimated
for 1992 through 2000. Spawning stock
biomass was 67% of fishable biomass in
2001, consistent with the 1986-2000
average.
Estimated lake whitefish biomass WFS-05
4000
3500
Total
Spawning Stock
3000
2500
2000
1500
1000
500
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
Estimates for total instantaneous
mortality rate (Z) have remained
consistently low since 1993.
The
-1
estimate for Z was 0.31 y in 2001.
63
Summary Status WFS-05 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.93 lb
4y
2.34 lb
5y
3.733 lb
(SE 0.007)
1.98 lb
(SE 0.08)
0.174 lb
(SE 0.000)
0.53
(SE 0.022)
0.739 lb
(SE 0.030)
Natural Mortality (M)
0.227 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
-1
11
11
-1
Average gill net F, ages 4+
0.025 y
(SE 0.002)
Average trap net F, ages 4+
0.083 y
(SE 0.008)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.334 y
(SE 0.01)
Recruitment (age-4)
(1992-2001 average)
293,700 fish
(SE 42,319)
Biomass (age 3+)
(1992-2001 average)
2,138,500 lb
(SE 207,730)
Spawning biomass
(1992-2001 average)
1,393,100 lb
(SE 121,310)
MSC recommended yield limit for 2003
Actual yield limit for 2003
64
745,000 lb
745,000 lb
WFS-06 (Grand Marais)
Prepared by Mark P. Ebener
WFS-06 is located in the center
of the 1836 treaty-ceded waters of Lake
Superior. The unit is part of the open
water of Lake Superior and contains no
islands or bays, and only a small amount
of water is <120 ft deep. There are only
88,600 surface acres of waters <240 ft
deep in the unit.
There is little habitat for
whitefish reproduction in WFS-06. The
entire shoreline is relatively straight and
is composed of sand with lesser amounts
of small-sized gravel and scattered
cobble that are found only on the
immediate shoreline. It is likely that
many of the lake whitefish that inhabit
WFS-06 may spawn elsewhere.
WFS-06 has been an exclusive
commercial fishing zone for CORA
fishers since 1985. Because the unit is
so exposed to the open water of Lake
Superior, and because access to the unit
is limited to the Grand Marais area, only
large-boat gill-net fisheries typically
operate here. A sizeable sport fishery
targets whitefish off the pier at Grand
Marais, but this yield and effort is not
included in the stock assessment model.
The commercial yield of lake
whitefish from WFS-06 has averaged
only 87,600 lb during 1985-2001. The
peak yield was 236,000 lb in 1990 and
the lowest yield was 26,000 lb in 1996.
The yield of whitefish was 33,600 lb in
2001.
Commercial lake whitefish yield WFS-06
250
Trap Net
GillNet
TAC
200
150
100
50
0
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
Year
The large-mesh gill-net fishery
has accounted for the entire yield from
WFS-06 since 1985. Effort averaged 2.7
million ft during 1985-2001 and ranged
from 5.3 million ft in 1990 to 0.5 million
ft in 1996. Large-mesh gill-net effort
has averaged only 1.4 million ft since
1996 and was 0.7 million ft in 2001.
Much of the gill-net effort in made up of
5 ¼ and 5 ½ inch stretched mesh.
Lake whitefish commercial trap net and gill net effort WFS-06
6.0
5.0
4.0
3.0
2.0
1.0
0.0
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Whitefish caught in WFS-06 are
large so the fishery targets them with the
large mesh because fishers are paid more
per pound for mediums and jumbos than
for No.1 whitefish. Annual mean weight
of whitefish in the gill-net yield from
WFS-06 ranged from 3.0 to 5.6 lb and
averaged 3.8 lb during 1985-2001.
Mean weight of whitefish in the gill-net
harvest averaged 5.3 lb in 2001. The
proportion of medium and jumbo
whitefish in the harvest from WFS-06 is
65
greater than nearly all other units in the
1836 ceded waters.
Growth of whitefish in WFS-06
has remained constant through time or
slightly increased. Mean weight of
nearly all age-classes in 2001 was equal
to or greater than prior to the mid 1980s.
estimated to be 317,000 lb in 2001.
Biomass averaged 414,000 lb during the
last decade in WFS-06.
Spawning
biomass has made up a larger proportion
of total biomass in the last few years
primarily because of the increases in
growth of whitefish in WFS-06.
Lake whitefish population mean weight at age WFS-06
Estimated lake whitefish biomass WFS-06
10.0
800
Age-6
Age-8
Age-10
Age-11+
9.0
8.0
7.0
Total
Spawning Stock
700
600
500
6.0
400
5.0
4.0
300
3.0
200
2.0
100
1.0
0
0.0
1985
1987
1989
1991
1993
1995
1997
1999
1985
2001
1987
1989
1991
1993
1995
1997
1999
2001
Year
Year
Recruitment to the fishable
population of whitefish in WFS-06 has
been declining through time based on the
stock assessment model. Recruitment of
age-4 whitefish was estimated to range
from 136,000 fish in 1988 to 11,000 in
2000. Recruitment was estimated to be
23,000 age-4 whitefish in 2001, which
represents an increase over 2000, but
still less than the long-term average of
50,000 fish.
Total annual mortality of
whitefish has declined through time
based on the stock assessment model.
Total mortality averaged only 0.32 y-1 on
age-4 and older whitefish in WFS-06
during 1999-2001 and was lower in 2001
than most other years. Fishing mortality
rate averaged 0.12 y-1 during 1999-2001
and was 0.09 y-1 in 2001. Because total
mortality was substantially less than the
target rate of 1.05 y-1 the projection
model estimated that fishing mortality
could be increased three times from the
current level to produce an annual
mortality of 0.71 y-1. The recommended
yield limit at the increased level of
fishing was estimated to be 98,000 lb.
Lake whitefish recruitment (age-4) WFS-06
160
140
120
100
80
60
40
Instantaneous mortality rates for lake whitefish WFS-06
20
0.8
0
0.7
1985
1987
1989
1991
1993
1995
1997
1999
2001
Natural
Gill Net
0.6
Year
0.5
0.4
0.3
Biomass of the fishable stock of
whitefish in WFS-06 has also declined
through time primarily because of
declines in recruitment to the fishery.
Biomass of whitefish peaked at 691,000
lb in 1988 and 493,000 lb in 1997.
Biomass of whitefish in WFS-06 was
0.2
0.1
0
1985
66
1987
1989
1991
1993
Year
1995
1997
1999
2001
Summary Status WFS-06 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.85 lb
4y
2.88 lb
5y
10.057 lb
(SE 0.002)
4.76 lb
(SE 0.44)
0.378 lb
(SE 0.000)
0.474
(SE 0.044)
1.406 lb
(SE 0.119)
-1
Natural Mortality (M)
0.198 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
7
-1
Average gill net F, ages 4+
0.118 y
(SE 0.019)
Average trap net F, ages 4+
0.0 y
(SE 0.0)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
-1
Average ages 4+,1999-2001
0.316 y
(SE 0.019)
Recruitment (age-4)
(1992-2001 average)
32,975 fish
(SE 3,041)
Biomass (age 3+)
(1992-2001 average)
414,390 lb
(SE 55,578)
Spawning biomass
(1992-2001 average)
345,080 lb
(SE 50,180)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
67
98,000 lb
98,000 lb
WFS-07 (Tahquamenon Bay)
Prepared by Mark P. Ebener
WFS-07 is located in the
Whitefish Bay area of Lake Superior.
The primary geographic feature of WFS07 is Whitefish Point. West and north of
Whitefish Point is the open water of
Lake Superior, while south of the Point
includes western Whitefish Bay and a
large amount of shallow water. WFS-07
contains 371,000 surface acres of water
less than 240 ft deep. There is a
substantial commercial fishery in
adjacent Canadian management unit 33.
WFS-07 contains a single, large
stock of whitefish that spawns in the
southwest portion of Whitefish Bay.
After spawning, whitefish disperse north
and west to Whitefish Point and areas of
the main part of Lake Superior. Many
whitefish also remain in Whitefish Bay
and some move into Canadian waters.
This unit is a very important
fishing ground for the CORA fishery,
and has been an exclusive CORA fishing
area since 1985. Large- and small-boat
gill-net fisheries as well as several trapnet fisheries operate in WFS-07. An ice
fishery also takes place nearly every
winter. There are a large number of
relatively good access sites to fishing
grounds in WFS-07 that offer fishermen
reasonable protection from wind and
waves.
The commercial yield of
whitefish from WFS-07 has averaged
411,000 lb during 1976-2001. A peak
yield of one million pounds occurred in
1990 and the lowest reported yield was
98,000 lb in 1977. The 2001 yield was
316,000.
Commercial lake whitefish yield WFS-07
1200
Trap Net
Gill Net
TAC
1000
800
600
400
200
0
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
Year
The large-mesh gill-net fishery
accounted for 76% of the whitefish yield
from WFS-07 during 1976-2001. Since
1998 the trap-net fishery has harvested
more whitefish from the unit than the
gill-net fishery, except in 2001. The
yield in 2001 was 240,000 lb from the
gill-net fishery and 76,000 lb from the
trap-net fishery.
Yield of whitefish from WFS-07
has mirrored changes in fishing effort
during 1976-2001. After peaking at 17.8
million ft in 1990, large-mesh gill-net
effort declined to between four and six
million ft during 1996-2001. Gill-net
effort was 5.8 million ft in 2001. Trapnet effort increased almost annually
from 128 lifts in 1985 to 1,161 lifts in
2000. Trap-net effort was only 175 lifts
in 2001 because several commercial
operations moved to fish in new areas of
Lake Huron after the 2000 Consent
Decree.
Lake whitefish commercial trap net and gill net effort WFS-07
1.4
20
Trap Net
Gill Net
1.2
18
16
1.0
14
12
0.8
10
0.6
8
6
0.4
4
0.2
2
0
0.0
1976
1979
1982
1985
1988
Year
68
1991
1994
1997
2000
Recruitment varied from 52,000 fish in
1976 to 628,000 fish in 1988. About
276,000 age-4 whitefish have recruited
to the fishable population each year
during 1992-2001. Recruitment was
estimated to be 154,000 age-4 whitefish
in 2001.
Whitefish caught in WFS-07 are
of moderate to large size. Mean weight
of a harvested whitefish averaged 3.2 lb
in the gill-net fishery and 2.8 lb in the
trap-net fishery during 1976-2001.
Mean weight of a harvested whitefish in
2001 averaged 3.6 lb in the gill-net
fishery and 3.2 lb in the trap-net fishery.
There have been two directional
changes in growth of whitefish in WFS07. From 1976-1990 mean weight-atage declined, particularly for whitefish
>age 6. Mean weight-at-age generally
increased for whitefish >age 6 in WFS07 after 1990.
Lake whitefish recruitment (age-4) WFS-07
700
600
500
400
300
200
100
0
Lake whitefish population mean weight at age WFS-07
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
12.0
10.0
8.0
Year
Age-4
Age-6
Age-8
Age-10
Average fishable biomass of age4 and older whitefish peaked at 3.6
million lb in 1989 and has declined and
stabilized since then. The fishable stock
biomass was 1.8 million lb in 2001,
compared to a spawning biomass of 1.9
million lb in 2001. Biomass declined by
600,000 lb from 1999 to 2000 and 2001,
and the 2001 biomass was equal to
levels observed in the mid 1980s in
WFS-07.
6.0
4.0
2.0
0.0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
Sexual maturity of whitefish in
WFS-07 occurs at a small size and
young age, but complete maturity of
females occurs at a large size and old
age. Female whitefish begin reaching
sexual maturity at age 3 and about 15
inches long, and by age 5 over 50% of
females are sexually mature. After age
5, however, the rate of sexual maturity
slows and complete maturity is not
achieved until whitefish reach 26 inches
long and age 12.
Estimated recruitment of age-4
whitefish to the fishable population has
gone through at least two significant
changes during 1976-2001. Recruitment
increased through time from 1976-1988,
thereafter, recruitment declined by onehalf and has been slowly declining since
1991. The stock assessment model
estimated that an average of 322,000
age-4 whitefish recruited to the fishable
population each year during 1976-2001.
Estimated lake whitefish biomass WFS-07
4000
Total
Spawning Stock
3500
3000
2500
2000
1500
1000
500
0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
Instantaneous
total
annual
mortality of age-4 and older whitefish
showed little change through time from
1976-2000.
The variations in total
mortality were driven largely by changes
in fishing effort, particularly large-mesh
gill-net effort.
Instantaneous total
annual mortality on age-4 and older fish
averaged 0.52 y-1 during 1976-2001.
Annual estimated mortality ranged from
69
0.71 y-1 in 1990 to 0.38 y-1 in 2001.
Fishing mortality averaged 0.34 y-1
during 1976-2001. Gill-net mortality
averaged 0.25 y-1 and trap-net mortality
0.09 y-1 during 1976-2001. Fishing
mortality in 2001 was 0.20 y-1, with gillnet mortality being 0.16 y-1 and trap-net
mortality 0.04 y-1.
Instantaneous mortality rates for lake whitefish WFS-07
1.0
0.9
0.8
0.7
Natural
Trap Net
Gill Net
Sea Lamprey
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
Since total annual mortality was
less than the target rate of 1.05 y-1 in
WFS-07 in 2001, the projection model
estimated that fishing mortality could be
increased 1.4 times from the levels
experience during 1999-2001. As a
consequence, the recommended yield
limit was estimated to be 502,000 lb.
The recommended yield limit was
302,000 lb in 2001 and 409,000 lb in
2000.
70
Summary Status WFS-07 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.68 lb
4y
2.21 lb
5y
7.958 lb
(SE 0.001)
2.16 lb
(SE 0.13)
0.291 lb
(SE 0.000)
0.271
(SE 0.016)
1.661 lb
(SE 0.015)
-1
Natural Mortality (M)
0.176 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
10
10
-1
Average gill net F, ages 4+
0.122 y
(SE 0.01)
Average trap net F, ages 4+
0.127 y
(SE 0.008)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.426 y
(SE 0.017)
Recruitment (age-4)
(1992-2001 average)
275,870 fish
(SE 10,185)
Biomass (age 3+)
(1992-2001 average)
2,259,400 lb
(SE 87,023)
Spawning biomass
(1992-2001 average)
2,092,900 lb
(SE 83,535)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
71
502,000 lb
502,000 lb
WFS-08 (Brimley)
Prepared by Mark P. Ebener
195,000 lb occurred in 1979, just prior to
the creation of CORA. The large-mesh
gill-net fishery accounted for 75% of the
whitefish yield from WFS-08 during
1981-2001. There was no trap-net yield
from WFS-08 during 1987-1995. The
trap-net yield in 2001 was 61,800 lb,
while the gill-net yield was 29,500 lb.
WFS-08 is located in the very
southeast portion of Whitefish Bay, Lake
Superior. Although WFS-08 is spatially
the smallest of the management units in
the 1836 ceded waters of Lake Superior
the unit contains 160,000 surface acres
of water <240 ft deep. A substantial
commercial fishery targeting whitefish
also exists in the adjacent Canadian
management units 33 and 34.
There
are
probably
four
reproductively isolated stocks of
whitefish that contribute to the
commercial
fishery
in
WFS-08.
Whitefish that spawn in WFS-07 are
caught in the commercial fishery of
WFS-08. The areas off Birch Point and
Iroquois Island are both whitefish
spawning grounds that contribute to the
fishery in WFS-08. A fourth spawning
population located in Canadian waters
off Gros Cap to the east of Iroquois
Point also contributes whitefish to the
fishery in WFS-08.
WFS-08 has been and continues
to be a traditional commercial fishing
area for the CORA small-boat and gillnet ice fishery. WFS-08 has been an
exclusive fishing zone for the CORA
fishery since 1985. There are seven or
eight undeveloped landing sites that are
commonly use by the CORA small-boat
fishery during the open-water fishing
season. A commercial trap-net fishery
and a sport fishery for whitefish also
occur in the unit.
The commercial yield of
whitefish from WFS-08 has averaged
95,700 lb during 1981-2001. Annual
yields ranged from 35,000 lb in 1983 to
188,000 lb in 1999. The peak yield of
Commercial lake whitefish yield WFS-08
200
Trap Net
Gill Net
TAC
180
160
140
120
100
80
60
40
20
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
Year
Gill-net effort has been declining
in WFS-08 while trap-net effort has
increased tremendously. Peak gill-net
effort was 4.1 million ft in 1989 but has
declined to an average of one million ft
during 1999-2001. Gill-net effort was
1.1 million ft in 2001. Trap-net effort
peaked at 738 lifts in 1979, declined to
zero during 1987-1995, and increased to
583 lifts in 2000. Trap-net effort was
268 lifts in 2001.
Lake whitefish commercial trap net and gill net effort WFS-08
7
4.5
Trap Net
4
Gill Net
6
3.5
5
3
4
2.5
3
2
1.5
2
1
1
0.5
0
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Whitefish in WFS-08 are of
moderate to large size. Mean weight of
72
Recruitment was estimated to be 74,000
age-4 whitefish in 2001.
a harvested whitefish in the gill-net
fishery averaged 3.0 lb and mean weight
in the trap-net fishery averaged 2.3 lb
during 1981-2001. Mean weight of a
harvested whitefish in 2001 was 2.5 lb in
the trap-net fishery and 2.7 lb in the gillnet fishery.
Growth in weight of whitefish in
WFS-08 has remained constant through
time unlike in other units of the 1836
ceded territory. There have been some
minor patterns in mean weight-at-age,
but for the most part growth has been
stable.
Lake whitefish recruitment (age-4) WFS-08
160
140
120
100
80
60
40
20
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Because whitefish in WFS-08
mature at a young age and small size,
fishable and spawning stock biomass
vary concurrently and are nearly equal.
Fishable stock biomass in WFS-08
averaged 466,000 lb during 1981-2001
and ranged from 241,000 lb in 1982 to
702,000 lb in 1988. Fishable stock
biomass was stable between 1992 and
2000 ranging from 438,000 lb to
594,000 lb. Both fishable and spawning
stock biomass was lower in 2001 than
the previous 15 years at 380,000 and
290,000 lb, respectively.
Lake whitefish population mean weight at age WFS-08
7.0
6.0
5.0
Age-4
Age-6
Age-8
Age-10
4.0
3.0
2.0
1.0
0.0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Whitefish in WFS-08 mature at
smaller sizes and ages than in WFS-07.
Female whitefish in WFS-08 begin
maturing at 15 inches total length and at
age 3. Two-thirds of whitefish in WFS08 are sexually mature by age 4.
Complete maturity is reached at 23
inches total length and age 11.
Recruitment of age-4 whitefish to
the fishable population in WFS-08 has
been less variable and stable than in
adjacent unit WFS-07.
The stock
assessment model estimated that an
average of 80,000 age-4 whitefish
recruited to the fishable population in
WFS-08 each year during 1981-2001.
Recruitment peaked in 1987 and 1988 at
137,000 and 119,000 age-4 fish,
respectively.
Thereafter, recruitment
was fairly stable ranging from 54,000 to
113,000
lb
during
1989-2001.
Estimated lake whitefish biomass WFS-08
800
700
Total
Spawning Stock
600
500
400
300
200
100
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
The large-mesh gill-net fishery
accounted for the largest single source of
mortality in whitefish from WFS-08.
Annual instantaneous total annual
mortality of age-4 and older whitefish
averaged 0.62 y-1 during 1981-2001 and
ranged from 0.43 y-1 to 1.02 y-1. Total
mortality rate was 0.65 y-1 in 2001.
Average gill-net mortality was 0.30 y-1
compared to 0.12 y-1 for the trap-net
73
fishery during 1981-2001. Trap-nets
were the largest single source of
mortality during 1999-2001. Trap-net
mortality was 0.26 y-1 and gill-net
mortality 0.20 y-1 in 2001.
Instantaneous mortality rates for lake whitefish WFS-08
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Natural
Trap Net
Gill Net
Sea Lamprey
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Total annual mortality on age-4
and older whitefish was less than the
target rate of 1.05 y-1 during 2000 and
2001. Unfortunately, the SPR value at
the target mortality rate was only 0.12
and less than the target SPR value of
0.20.
Thus the projection model
estimated that fishing mortality rate
should be reduced 42% from levels
experienced during 1999-2001. The
recommended yield limit was estimated
to be 67,000 lb in 2003.
The
recommended yield limit was 176,000 in
2001 and 81,000 lb in 2002. A harvest
regulating guideline of 87,000 lb was
used as the yield limit for 2003 and
represents the average yield during
1999-2002.
74
Summary Status WFS-08 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.43 lb
4y
2.04 lb
5y
5.489 lb
(SE 0.01)
0.72 lb
(SE 0.03)
0.168 lb
(SE 0.000)
0.132
(SE 0.006)
1.308 lb
(SE 0.003)
-1
Natural Mortality (M)
0.197 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
10
10
-1
Average gill net F, ages 4+
0.152 y
(SE 0.014)
Average trap net F, ages 4+
0.446 y
(SE 0.025)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
-1
Average ages 4+,1999-2001
0.795 y
(SE 0.036)
Recruitment (age-4)
(1992-2001 average)
79,570 fish
(SE 3,364)
Biomass (age 3+)
(1992-2001 average)
513,550 lb
(SE 16,985)
Spawning biomass
(1992-2001 average)
484,920 lb
(SE 15,855)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG = 1999-2002 average yield)
75
67,000 lb
87,000 lb
Lake Huron
WFH-01 (St. Ignace)
Prepared by Mark P. Ebener
The large-mesh gill-net fishery
has accounted for the majority of the
commercial yield from WFH-01 during
1976-2001.
From 1976-1984 largemesh gill nets accounted for 0-41% of
the annual fishery yield, while after 1985
gill-net accounted for 52-81% of the
annual yield.
The gill-net fishery
accounted for 67% of the commercial
yield of lake whitefish from WFH-01
during 1992-2001. The gill-net fishery
harvested 154,000 lb in 2001 compared
to 72,000 for the trap-net fishery.
Both gill-net and trap-net fishing
effort has been declining in WFH-01.
Trap-net effort peaked at 1,357 lifts in
1981 and since then it has declined
almost annually reaching a low of 98
lifts in 2001. Gill-net effort was stable
at about 4 million ft from 1983 to 1993,
increased to 10.5 million ft in 1996, and
has declined since to 4.1 million ft in
2001.
Management unit WFH-01 is
located in the northwest portion of the
main basin of Lake Huron. The unit is
relatively shallow as most water is <150
ft deep. WFH-01 contains 232,275
surface acres of water <240 ft deep.
There are probably several
reproductively isolated stocks of lake
whitefish that inhabit WFH-01. One
stock is located near Cheboygan, MI,
another stock spawns north of St. Ignace
near Rabbitsback and Horseshoe Bay,
and third stock spawns in St. Martin
Bay. A fourth stock probably spawns
near Hessel, MI.
WFH-01 has been an exclusive
fishing zone for the CORA fishery since
1985 and is a favored fishing area for
small-boat gill-net fishers, especially
during the early spring and fall. In most
years some gill-net fishing occurs under
the ice in St. Martin Bay. Commercial
fishery yield has ranged from a low of
46,000 lb in 1977 to 806,000 lb in 1994
and averaged 495,000 lb during 19922001.
The commercial yield was
226,000 lb in 2001 compared to 428,000
lb in 2000 and the commercial yield in
2001 was less than the recommended
harvest limit of 327,000 lb.
Lake whitefish commercial trap net and gill net effort WFH-01
16
12
Trap Net
Gill Net
14
10
12
8
10
6
8
6
4
4
2
2
Commercial lake whitefish yield WFH-01
900
0
0
1976
Trap Net
GillNet
TAC
800
700
400
300
200
100
0
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
Whitefish in WFH-01 are of
small size with over 90% of the harvest
by weight being made up of No1 fish
(<3 lb). Mean weight of whitefish in the
trap-net fishery ranged from 2.1 to 2.3 lb
during 1992-2001. Mean weight of
whitefish in the gill-net fishery ranged
500
1978
1980
Year
600
1976
1978
2002
Year
76
from 2.2 to 2.5 lb during 1992-2001.
Mean weight of a harvested whitefish
was 2.3 lb in the gill-net fishery and 2.1
lb in the trap-net fishery in 2001.
Growth of lake whitefish,
expressed as mean weight at age,
continued to decline in WFH-01 during
2001. The decline in mean weight at age
has been most pronounced for whitefish
of age 5 and older, while growth of
younger fish appeared to stabilize in
2001.
Lake whitefish recruitment (age-3) WFH-01
1200
1000
800
600
400
200
0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
Because of the declines in
growth and recruitment in WFH-01,
biomass declined to a low level in 2001.
Spawning stock biomass of whitefish in
WFH-01 has always been considerably
less than total biomass, in comparison to
some other units in Lake Huron, but the
biomass of one million lb in 2001 was
lower than all years except prior to 1979.
Total stock biomass declined from 2.4
million lb in 2000 to 1.8 million lb in
2001.
Lake whitefish population mean weight at age WFH-01
7
Age-3
Age-5
Age-7
Age-9
6
5
4
3
2
1
0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
The decline in growth has had a
profound effect on sexual maturity of
whitefish in WFH-01. The proportion of
sexually mature age-4 female whitefish
declined from 66% during 1976-1982 to
45% during 1983-1992, then to 24%
during 1993-2000. Only 3% of age-4
female whitefish were sexually mature
in 2001.
Large year-classes of whitefish
were produced during 1987-1994 in
WH-01, and then recruitment declined.
These large year-classes produced the
large yield of 806,000 lb in 1994 and
also probably helped suppress growth of
whitefish in the unit. The long-term
trend in recruitment in WFH-01 appears
be one of stable and good recruitment
for 8-9 yr then declines of 3-4 yr before
increasing again.
Estimated lake whitefish biomass WFH-01
4500
4000
Total
Spawning Stock
3500
3000
2500
2000
1500
1000
500
0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
The large-mesh gill-net fishery
has been the single largest source of
fishing mortality on whitefish in WFH01. Gill- net fishing mortality rate of
age-4 and older whitefish ranged from
0.0 y-1 to 0.45 y-1 during 1976-2001,
whereas trap-net fishing mortality rate
ranged from 0.04y-1 to 0.31 y-1 during
1976-2001 on age-4 and older fish. Gillnet fishing mortality rate averaged was
0.18 y-1 and trap-net fishing mortality
rate average 0.05 y-1 during 1999-2001.
77
Instantaneous mortality rates for lake whitefish WFH-01
1.0
Natural
Trap Net
Gill Net
Sea Lamprey
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
Natural mortality rate, including
sea lamprey-induced mortality, was
greater than fishing mortality during the
last five years in WFH-01. Natural
mortality including sea lamprey
mortality ranged from 0.29 y-1 to 0.36 y-1
during 1997-2001, whereas total fishing
mortality rate declined from 0.35 y-1 in
1997 to 0.14 y-1 in 2001. From 1997 to
2001 natural mortality averaged 0.23 y-1,
gill-net mortality 0.19 y-1, sea lamprey
morality 0.08 y-1 and trap-net mortality
0.06 y-1 on age-4 and older whitefish.
Sea Lamprey Mortality
Sea lamprey mortality ages 4+ WFH-01
0.6
4
0.5
5
6
0.4
7
0.3
8
9
0.2
10+
0.1
0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
The current spawning potential
reduction value of 0.26 in WFH-01
during 1999-2001 was greater than the
minimum value of 0.20 as defined by the
modeling subcommittee.
Thus, the
projection model estimated that fishing
mortality rate could be increased 1.65
times from the 1999-2001 values. The
increase in fishing effort produced a
recommended yield limit of 375,000 lb
round weight, an increase from the
248,000 lb limit in 2002.
78
Summary Status WFH-01 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.42 lb
3y
1.81 lb
6y
1.526 lb
(SE 0.003)
0.4 lb
(SE 0.02)
0.039 lb
(SE 0.000)
0.259
(SE 0.011)
0.458 lb
(SE 0.014)
-1
0.233 y
Natural Mortality (M)
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
9
9
-1
Average gill net F, ages 4+
0.178 y
(SE 0.018)
Average trap net F, ages 4+
0.046 y
(SE 0.003)
-1
Sea lamprey mortality (ML)
-1
(average ages 4+,1999-2001)
0.073 y
Average ages 4+,1999-2001
0.531 y
(SE 0.017)
Total mortality (Z)
-1
Recruitment (age-3)
(1992-2001 average)
760,820 fish
(SE 44,839)
Biomass (age 3+)
(1992-2001 average)
3,326,500 lb
(SE 114,700)
Spawning biomass
(1992-2001 average)
2,015,200 lb
(SE 71,679)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
375,000 lb
375,000 lb
79
WFH-02 (Detour)
Prepared by Mark P. Ebener
The allocation of the harvest
among fishing gears has changed
dramatically in WFH-02 over the past
few years. From 1985 through 1997 the
large-mesh gill-net fishery accounted for
majority of harvest in every year. After
1997 the trap-net fishery accounted for
the largest proportion of the harvest. The
trap-net fishery harvested 262,000 lb of
whitefish in 2001, while the gill-net
fishery harvested only 54,000 lb. The
gill-net yield in 2001 was lower than
every other year except 1982 when the
CORA fishery began in WFH-02.
Both large-mesh gill-net and trapnet effort have changed markedly in
WFH-02 since 1980. Trap-net effort
ranged from 0 to 713 lifts between 1980
and 1997, thereafter effort increased
2,033 lifts in 1999, then declined by half
in 2000 and 2001. Large-mesh gill-net
effort increased from zero in 1981 to 7.2
million ft in 1995, since then gill-net
effort has declined to 2.0 million ft in
2001.
Management unit WFH-02 is
located along the northern shore of the
main basin of Lake Huron. Much of
WFH-02 is deeper than 150 ft and
maximum depth is slightly greater than
300 ft. WFH-02 is a small unit that is
made up of only three statistical grids and
contains 122,562 surface acres of water
<240 ft deep. The unit has an irregular
shoreline with many small, rocky points,
isolate bays, and scattered boulders.
Because the shoreline of WFH-02
is highly irregular and rocky, nearly the
entire unit contains habitat suitable for
reproduction and survival of young.
Spawning concentrations of whitefish can
be found throughout the unit from
Beavertail Point in the west portion of the
unit to St. Vitals Point in the middle of
the unit. This area covers roughly 16
miles of shoreline or more. A large
aggregation of spawning whitefish can be
found in the area from Albany Island to
Saddle Bag Islands.
WFH-02 has been a CORA
exclusive fishing zone since the 1985
Consent Decree. The commercial yield
of lake whitefish ranged from a low of
152,000 lb in 1980 to 888,000 lb in 1998.
The fishery yield averaged 534,000 lb
during 1922-2001. The yield of whitefish
from WFH-02 declined from 773,000 lb
in 1999 to 408,000 lb in 2000 and to
316,000 lb in 2001.
Lake whitefish commercial trap net and gill net effort WFH-02
8
25
Trap Net
Gill Net
6
5
15
4
10
3
2
5
1
0
0
1980
Commercial lake whitefish yield WFH-02
700
600
500
400
300
200
100
0
1980
1982
1984
1986
1988
1990
1992
1994
1996
1984
1986
1988
1990
1992
1994
1996
1998
2000
Whitefish in WFH-02 have
always been of small size. No. 1 fish
make up 90% of the harvest in from the
unit.
Mean weight in the trap-net
harvest has ranged from 2.0 to 2.3 lb and
mean weight in the gill-net harvest
ranged from 1.9 to 2.8 lb during 19922001. Mean weight of a harvested
whitefish was 2.2 lb in the trap-net
Trap Net
GillNet
TAC
800
1982
Year
1000
900
7
20
1998
2000
2002
Year
80
fishery and 2.8 lb in the gill-net fishery in
2001.
A distinct characteristic of
whitefish in WFH-02 is their small size at
sexual maturity.
Some females are
sexually mature by 14 inches long and
50% are sexually mature at 15.7 inches
long. Age at first maturity begins at age3 and 90% are sexually mature by age-7.
Unlike other units in Lake Huron,
growth of whitefish in WFH-02 has
remained stable through time. There has
been a slight decline mean weight at age
since the early 1980s, but the declines
have not been nearly as steep as in WFH01, WFH-04, and WFH-05.
Lake whitefish recruitment (age-4) WFH-02
1400
1200
1000
800
600
400
200
0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
The large increase in recruitment
during the mid 1990s more than doubled
biomass of whitefish in WFH-02.
Fishable biomass of whitefish in WFH-02
increased from 1.5 million lb in 1990 to
4.2 million lb in 1996 and 1997. Fishable
and spawning stock biomass are nearly
equivalent in WFH-02 because the fish
mature at such a small size and because
growth has not declined much. Fishable
biomass was estimated to be 1.4 million
lb and spawning biomass 1.1 million lb in
2001.
Lake whitefish population mean weight at age WFH-02
6
Age-4
Age-6
Age-8
Age-10
5
4
3
2
1
Estimated lake whitefish biomass WFH-02
0
5000
1980
1982
1984
1986
1988
1990 1992
Year
1994
1996
1998
2000
4500
4000
The substantial increase in
commercial fishery yield during the mid
1990s in WFH-02 was driven largely by
increased recruitment. The 1988-1993
year classes of whitefish were
substantially larger than preceding and
subsequent year classes in WFH-02. The
stock assessment model estimated that the
1991-year class contained 1.26 million
fish when it recruited to the fishery at age
4 in 1995. The 1989, 1990, 1992, and
1993 year classes contained between
895,000 and 1.1 million age-4 whitefish
when they recruited to the fishery. Prior
to 1992 and after 1997 most year classes
that recruited to the fishery at age 4 did
not exceed 600,000 fish. The 1997 year
class was estimated to contain only
323,000 fish at age 4 when it recruited in
2001.
Total
Spawning Stock
3500
3000
2500
2000
1500
1000
500
0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Year
Total annual mortality rate on
age-4 and older whitefish in WFH-02 has
increased nearly annually since 1980.
Total annual mortality of age-4 and older
whitefish nearly doubled from 0.47 y-1 in
1980 to 0.92 y-1 in 1999.
81
the projection model estimated a
recommended yield limit of 221,000 lb.
The harvest regulating guideline was set
at 340,000 lb and represents the average
harvest during 1999-2002.
Instantaneous mortality rates for lake whitefish WFH-02
1.0
0.9
0.8
0.7
Natural
Trap Net
Gill Net
Sea Lamprey
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1980
1982
1984
1986
1988
1990 1992
Year
1994
1996
1998
2000
The increase in total mortality was
due to the substantial increases in fishing
effort through 1999 and because of
increased sea lamprey predation since
1990. Prior to 1997 trap-net mortality
ranged from 0.02 y-1 to 0.23 y-1, while
after 1997 trap-net mortality ranged from
0.25 y-1 to 0.42 y-1. Gill-net mortality
ranged from 0.0 y-1 to 0.46 y-1 prior to
1997 and from 0.07 y-1 to 0.30 y-1
thereafter. Gill-net mortality was 0.07 y-1
and trap-net mortality was 0.25 y-1 in
2001. Sea lamprey mortality averaged
0.07 y-1 from 1990-2001, but increased
from 0.07 y-1 in 1990 to 0.16 y-1 in 2000.
Sea Lamprey Mortality
0.6
0.5
0.4
Sea lamprey mortality ages 4+ WFH-02
4
5
6
7
8
0.3
0.2
9
10+
0.1
0.0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Total annual mortality of age-4
and older whitefish averaged 0.875 y-1
during 1999-2001, but mortality on fully
vulnerable ages-9 and older exceeded the
target rate of 1.05 y-1.
Spawning
potential reduction at the current
mortality rates was 0.51 and considerably
greater than the target of 0.20. The
projection model estimated that fishing
mortality rate should be reduced 43% to
achieve the target mortality rate on older
ages classes even though the SPR was
greater than target. As a consequence,
82
Summary Status WFH-02 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.98 lb
4y
1.44 lb
5y
2.076 lb
(SE 0.004)
0.51 lb
(SE 0.02)
0.111 lb
(SE 0.000)
0.247
(SE 0.009)
0.632 lb
(SE 0.009)
-1
Natural Mortality (M)
0.267 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
9
9
-1
Average gill net F, ages 4+
0.124 y
(SE 0.013)
Average trap net F, ages 4+
0.361 y
(SE 0.024)
-1
Sea lamprey mortality (ML)
-1
(average ages 4+,1999-2001)
0.123 y
Average ages 4+,1999-2001
0.875 y
(SE 0.035)
Total mortality (Z)
-1
Recruitment (age-4)
(1992-2001 average)
730,440 fish
(SE 28,969)
Biomass (age 3+)
(1992-2001 average)
3,098,100 lb
(SE 93,724)
Spawning biomass
(1992-2001 average)
2,781,200 lb
(SE 80,388)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG = 1999-2002 average yield)
83
221,000 lb
340,000 lb
WFH-03 (Drummond Island)
Prepared by Mark P. Ebener
lb in 2001. Ninety-eight percent of the
yield was taken with trap-nets during
1999-2001.
Management unit WFH-03 is a
small area that encompasses the area
around Drummond Island. A lake trout
refuge is located along the south shore of
Drummond Island where large-mesh
gill-net fishing is prohibited and
retention of lake trout by trap-net
fisheries is prohibited. The south side of
WFH-03 is deep with much of the water
exceeding 150 ft deep, whereas the north
and west sides of Drummond Island are
relatively shallow and part of the North
Channel and St. Marys River. WFH-03
contains six statistical grids and
<100,000 surface acres of water <240 ft
deep.
All of WFH-03 lies within the
Niagara Escarpment and is composed of
dolomite limestone.
The spawning
shoals for lake whitefish in WFH-03 are
located primarily along the south shore
of Drummond Island in the main basin
of Lake Huron. Adult whitefish in
spawning condition have been caught
primarily between Seaman Point and Big
Shoal by CORA staff during gill-net
surveys in October of 1991-2001.
WFH-03 has been an exclusive
fishing zone for the CORA fishery since
1985. The unit is primarily a trap-net
fishery. A winter gill-net fishery of
whitefish takes place under the ice in the
North Channel from January through
early March of most years. The trap-net
fishery takes place year-round along the
south shore of Drummond Island since
ice seldom forms here.
The commercial yield of lake
whitefish from WFH-03 has increased
tremendously since 1998. Prior to 1998
the commercial yield of lake whitefish
exceeded 100,000 lb only once in 1985.
After 1998 the commercial yield from
WFH-03 increased to 221,000 lb in
1999, 295,000 lb in 2000, and 370,000
B io m a s s (1 0 0 0 s lb )
Commercial lake whitefish yield WFH-03
400
350
300
250
200
150
100
50
0
Gill net
Trap net
1976 1979 1982 1985 1988 1991 1994 1997 2000
The large-increase in harvest in
WFH-03 during 1999-2001 was directly
related to increased trap-net effort.
Trap-net effort ranged from 0 to 392 lifts
in WFH-03 during 1976-1997, thereafter
trap-net effort increased to 673 lifts in
1999, 806 lifts in 2000, and 706 lifts in
2001. Gill-net effort was highly variable
in WFH-03 ranging from 0 to 162,000 ft.
during 1976-2001.
T h o u sa n d s o f fe et
o f g ill n et
200
150
Gill net
1,000
Trap net
800
600
100
400
50
200
0
0
1976
1980
1984
1988
1992
1996
N u m b e r o f tr a p n et lifts
Lake whitefish commerical trap net and gill net effort WFH-03
2000
Year
Whitefish caught in the fishery of
WFH-03 are moderate size. During
1987-2001 67% of the whitefish
harvested were No. 1 fish, 25% were
mediums (3-4 lb) and 8% were jumbos
(>4 lb). Mean weight of whitefish in the
trap-net harvest ranged from 2.0 to 2.8 lb
and average 2.7 lb during 1991-2001.
Mean weight in the gill-net fishery
ranged from 2.3 to 3.0 lb and averaged
2.7 lb.
84
Sea lamprey-induced mortality
rate has been declining in WFH-03 since
1991 and after a short peak in 1999. Sea
lamprey mortality of age-4 and older
whitefish was <0.02 y-1 during 19871990, increased to 0.17 y-1 in 1991, then
declined to 0.0 y-1 in 1997. Sea lamprey
mortality peaked at 0.27 y-1 in 1999 then
declined to 0.03 y-1 in 2001.
Growth of whitefish in WFH-03
has declined through time, but not at the
rate that has occurred in more western
areas of Lake Huron. Mean weight at
age 4, 6, 8, and 10+ did decline during
1991-2001 based on catches made
during CORA graded-mesh gill-net
surveys and monitoring of commercial
trap-net catches.
Sea lamprey mortality ages 4+ WFH-03
4
6
8
8.0
Pounds
Sea Lamprey M ortality (M l)
Population Mean Weight at Age WFH-03
10.0
6.0
10+
4.0
2.0
0.0
4
0.5
5
0.4
6
0.3
7
8
0.2
0.1
9
10+
0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Year
Year
Reasonable
estimates
of
abundance and mortality could not be
produced with the stock assessment
model for WFH-03. The model results
were very unstable and changed by an
order of magnitude in some cases after
only small changes were made to input
parameters of starting values.
A harvest regulating guideline of
318,000 lb was established for WFH-03
in 2003 and represents the average yield
during 1999-2002 from the unit. The
harvest regulating guideline was 293,000
lb in 2002 and 220,000 to 250,000 lb in
2001.
Recruitment of whitefish in
WFH-03 appears very similar to that in
WFH-02. The 1987-1995 year classes
were very abundant, whereas the 1996
and 1997 year classes, as well as the
1985 and 1986 year classes, were not
very abundant based on CPUE in CORA
gill-net surveys in WFH-03. The 1998
year class appears to be of reasonable
size based on survey catches.
Whitefish Year Class Strength WFH-03
20
C P U E A g es 2 -1 3
0.6
15
10
5
0
1978 1981 1984 1987 1990 1993 1996 1999
Year Class
85
WFH-04 (Hammond Bay)
Prepared by Mark P. Ebener
WFH-04 is the largest whitefish
management unit in the 1836 treatyceded waters of Lake Huron. The unit
contains 377,567 surface acres of water
<240 ft deep. Spawning concentrations
of whitefish are scattered throughout the
unit with concentrations being found
from Cheboygan, MI to Hammond Bay.
In August 2000 WFH-04 became
an exclusive CORA commercial fishing
zone. Prior to 2000 the area south of 40
Mile Point was an exclusive commercial
fishing zone for state-licensed trap-net
fisheries, while the area north of 40 Mile
Point was an exclusive CORA
commercial fishing zone since 1985.
The CORA large-mesh gill-net
fishery accounted for the majority of the
whitefish harvest from the unit from
1985-2000. In 2001 the trap-net harvest
from WFH-04 exceeded the gill-net
harvest for the first time since 1981.
The annual yield ranged from a high of
1.2 million lb in 1989 to a low of
231,000 lb in 1981. The annual yield of
whitefish from the unit averaged
810,000 lb during 1992-2001. The trapnet harvest of whitefish was 396,000 lb
in 2001 compared to 228,000 lb for the
large-mesh gill-net fishery. The 2001
yield of 624,000 lb was substantially less
than the harvest regulating guideline of
787,000 lb, but substantially greater than
the recommended harvest limit of
263,000 lb generated by the projection
model.
Commercial lake whitefish yield WFH-04
1400
Trap Net
GillNet
TAC
1200
1000
800
600
400
200
0
Year
Trap-net effort increased while
gill-net effort declined from 2000 to
2001. Large-mesh gill-net effort peaked
at 7.7 million ft in 1989 and 5.2 million
ft in 2000. Large-mesh gill-net effort
was 3.5 million ft in 2001. Trap-net
effort peaked at 719 lifts in 1992 then
declined to 308 lifts in 1999. Trap-net
effort increased from 358 lifts in 2000 to
972 lifts in 2001. The changes in fishing
effort occurred largely because two
CORA trap-net operations began fishing
in WFH-04 during 2001 as part of the
gear conversion program stipulated in
the 2000 Consent Decree.
Lake whitefish commercial trap net and gill net effort WFH-04
12
10
10
9
8
7
6
5
4
3
2
1
0
Trap Net
Gill Net
8
6
4
2
0
Year
Whitefish from WFH-04 are of
moderate size. The commercial harvest
from WFH-04 was composed of 65%
No. 1 whitefish (<3.0 lb), 26% mediums
(3-4 lb), and 9% jumbos (>4.0 lb) during
1982-2001. Annual mean weight of
whitefish caught in the gill-net fishery
ranged from 2.6 to 3.0 lb during 19822001, while mean weight in the trap-net
86
fishery ranged from 2.4 to 3.6 lb during
1982-2001. Mean weight in the harvest
in 2001 was 2.4 lb for the trap-net
fishery and 2.6 lb for the gill-net fishery.
Growth rate of whitefish from
WFH-04 continues to decline. Only
mean weight of age-9 and older
whitefish increased from 2000 to 2001.
Mean weight of ages 3-8 was lower in
2001 than any other year during 19812001.
Lake whitefish recruitment (age-3) WFH-04
2000
1800
1600
1400
1200
1000
800
600
400
200
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
The combined effects of reduced
recruitment and growth has meant that
biomass of whitefish in WFH-04 was
lower in 2001 than any other year during
last 21 yr. After peaking at 8.1 million
lb in 1994, fishable biomass declined
annually to only 1.7 million lb in 2001.
Spawning stock biomass declined from
4.3 million lb in 1995 to 1.1 million lb in
2001. Given that the 1998 year class
does not appear to be very abundant,
biomass of whitefish in WFH-04 can be
excepted to continue to decline.
Lake whitefish population mean weight at age WFH-04
8
Age-3
Age-5
Age-7
Age-9
7
6
5
4
3
2
1
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
The declines in harvest from
WFH-04 that have occurred from 1996
to 2001 are largely being driven by
declines in both mean weights at age and
recruitment. The 1988-1991 year classes
of whitefish were very abundant in
WFH-04. Recruitment to the fishery at
age 3 ranged from 1.4 to 1.9 million fish
for
these
four
year
classes.
Unfortunately, recruitment declined
dramatically after the 1991 year class
and the 1995-1997 year classes were the
least abundant as they recruited at age 3
to the fishery in WFH-04. Abundance
at age 3 for the 1995-1997 year classes
ranged from 228,000 to 364,000 fish.
The 1998 year class was estimated to
contain 335,000 fish when it recruited to
the fishery in 2001.
Estimated lake whitefish biomass WFH-04
9000
8000
7000
Total
Spawning Stock
6000
5000
4000
3000
2000
1000
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Total annual mortality of age-4
and older whitefish averaged 0.548 y-1
during 1999-2001.
Gill-net fishing
mortality averaged 0.201 y-1, trap-net
fishing mortality 0.136 y-1, and sea
lamprey mortality 0.04 y-1 during 19992001. Sea lamprey-induced mortality
was substantially less in WFH-04 than in
other more northerly units in Lake
Huron averaging less than 0.1 y-1 during
1981-2001. Gill-net mortality was 0.13
y-1, trap-net mortality 0.21 y-1, and sea
lamprey mortality 0.02 y-1 on age-4 and
older whitefish in 2001.
87
Since total annual mortality on
all age classes of whitefish was less than
the target of 1.05 y-1, the projection
model estimated that fishing mortality
rate could be increased 1.34 times in
2003 over that experienced during 19992001. The SPR value at the targetfishing rate was 0.184.
The
recommended harvest rate from the
projection model was 333,000 lb, but the
harvest regulating guideline for WFH-04
was set at 588,000 lb for 2003.
Instantaneous mortality rates for lake whitefish WFH-04
1.0
Natural
Trap Net
Gill Net
Sea Lamprey
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Sea lamprey mortality ages 4+ WFH-04/05
0.6
Sea Lamprey Mortality
4
0.5
0.4
0.3
5
6
7
8
9+
0.2
0.1
0.0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
88
Summary Status WFH-04 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.50 lb
3y
1.78 lb
6y
1.916 lb
(SE 0.)
0.35 lb
(SE 0.02)
0.108 lb
(SE 0.000)
0.184
(SE 0.012)
0.679 lb
(SE 0.006)
-1
Natural Mortality (M)
0.224 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
8
8
-1
Average gill net F, ages 4+
0.201 y
(SE 0.014)
Average trap net F, ages 4+
0.136 y
(SE 0.012)
-1
Sea lamprey mortality (ML)
-1
(average ages 4+,1999-2001)
0.041 y
Average ages 4+,1999-2001
0.548 y
(SE 0.022)
Total mortality (Z)
-1
Recruitment (age-3)
(1992-2001 average)
837,270 fish
(SE 26,160)
Biomass (age 3+)
(1992-2001 average)
5,422,800 lb
(SE 162,960)
Spawning biomass
(1992-2001 average)
2,876,100 lb
(SE 106,460)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG = 1999-2002 average yield)
89
333,000 lb
588,000 lb
WFH-05 (Alpena)
Prepared by Mark P. Ebener
WFH-05 runs from Presque Isle
south to North Point and includes some
waters of Lake Huron that lie outside the
1836-ceded waters.
There are an
estimated 209,000 surface acres of water
< 240 ft deep in WFH-05. WFH-05
contains a large spawning stock of
whitefish that spawns essentially
throughout the unit.
The 2000 Consent Decree
converted WFH-05 from an exclusive
state zone to an exclusive CORA trapnet fishing zone beginning in August
2000.
Only four CORA trap-net
operations from two tribes can fish
WFH-05, and each operation can fish no
more than 12 trap-nets. The CORA
fishery has a 17-inch minimum length
limit, and there is no limit on the depth
of water in which trap-nets can be
fished. There was a 19-inch minimum
length limit, and trap-nets could only be
fished in waters < 90 ft deep when
WFH-05 was an exclusive state zone.
Annual commercial trap-net
yields have ranged from 124,000 lb in
1981 to 736,000 lb in 2001 and averaged
455,000 lb during 1981-2001. The
changes in harvest are directly related to
changes in trap-net effort. As trap-net
effort increased from 130 lifts in 1991 to
566 lifts in 2001, the yield increased
from 322,000 lb in 1991 to 736,000 lb in
2001.
Lake whitefish commercial trap net and gill net effort WFH-05
500
7
Trap Net
Gill Net
6
450
400
5
350
300
4
250
3
200
150
2
100
1
50
0
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Whitefish in WFH-05 are of
similar size to those in WFH-04. The
commercial harvest from WFH-05 was
made up of 70% No. 1 whitefish, 23%
mediums, and 7% jumbos. Mean weight
of a harvested whitefish was 2.6 lb in
WFH-05 in 2001.
Growth rate of whitefish in
WFH-05 has stabilized over the last few
years after continually declining from
1981 to 1999. Prior to 1985 age-9 and
older whitefish weighed between 7 and 8
lb, but by 1999 they weighed about 3.3
lb. Mean weight of all age-classes in
2001 was similar to mean weight in
1999 and 2000.
Lake whitefish population mean weight at age WFH-05
9
8
7
Age-3
Age-5
Age-7
Age-9
6
5
4
3
2
1
Commercial lake whitefish yield WFH-05
1000
0
900
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Trap Net
GillNet
TAC
800
700
600
500
400
300
200
100
0
1981
1983
1985
1987
1989
1991
1993
Year
1995
1997
1999
2001
Recruitment of age-3 whitefish to
the fishable population in WFH-05
appears to have stabilized over the last
few years. Recruitment peaked at 2.4
million age-3 whitefish in 1989 and then
declined annually to about one million
age-3 whitefish in 1996 (1993 year
class).
From 1997 through 2001
90
older whitefish in WFH-05. Natural
mortality was greater than fishing and
sea lamprey mortality combined in all
years in WFH-05 and was estimated to
be 0.319 y-1. Trap-net fishing mortality
has been increasing in WFH-05 over the
last decade and was 0.20 y-1 in 2001.
Sea lamprey mortality has also generally
been increasing in WFH-05 over the last
decade, but it did not exceed 0.05 y-1 in
any year.
estimated recruitment averaged about
1.35 million age-3 whitefish. The stock
assessment model estimated that 1.49
million age-3 whitefish were present in
the population during 2001.
Lake whitefish recruitment (age-3) WFH-05
3000
2500
2000
1500
1000
Instantaneous mortality rates for lake whitefish WFH-05
500
1.0
Natural
Trap Net
Gill Net
Sea Lamprey
0.9
0
0.8
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
0.7
Year
0.6
Both fishable and spawning stock
biomass has been declining in WFH-05
since the early 1990s primarily because
of reduced recruitment and growth.
Fishable stock size peaked at 9.1 million
lb in 1992 and has since declined to 4.9
million lb in 2001. Spawning stock
biomass peaked at 6.6 million lb in 1993
and then declined to 2.8 million lb in
2001.
0.5
0.4
0.3
0.2
0.1
0.0
Year
Total annual mortality was
estimated to be only 0.547 y-1 on age-4
and older whitefish in WFH-05 during
1999-2001.
Total mortality was
estimated to be 0.581 y-1 in 2001.
Because total mortality was less than the
target rate of 1.05 y-1, the projection
model estimated that trap-net fishing
effort could be increased 1.95 times over
the
1999-2001
levels.
The
recommended yield limit at this
increased rate of fishing was estimated
to be 875,000 lb in WFH-05 for 2003.
The recommended yield limit in 2002
was estimated to be 670,000 lb.
Estimated lake whitefish biomass WFH-05
10000
9000
Total
Spawning Stock
8000
7000
6000
5000
4000
3000
2000
1000
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Natural
mortality
has
consistently been the most significant
source of mortality affecting age-4 and
91
Summary Status WFH-05 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.47 lb
3y
2.22 lb
6y
1.131 lb
(SE 0.)
0.49 lb
(SE 0.03)
0.155 lb
(SE 0.000)
0.437
(SE 0.027)
0.421 lb
(SE 0.026)
Natural Mortality (M)
0.319 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
-1
8
8
-1
Average gill net F, ages 4+
0.002 y
(SE 0.0)
Average trap net F, ages 4+
0.185 y
(SE 0.027)
-1
Sea lamprey mortality (ML)
-1
(average ages 4+,1999-2001)
0.041 y
Average ages 4+,1999-2001
0.547 y
(SE 0.027)
Total mortality (Z)
-1
Recruitment (age-3)
(1992-2001 average)
1,260,200 fish
(SE 137,370)
Biomass (age 3+)
(1992-2001 average)
6,545,000 lb
(SE 642,080)
Spawning biomass
(1992-2001 average)
4,946,300 lb
(SE 495,730)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
92
875,000 lb
875,000 lb
Lake Michigan
WFM-01 (Bays de Noc)
Prepared by Philip J. Schneeberger
being a very important area for lake
whitefish reproduction that exhibits
fairly consistent favorable conditions
resulting in relatively stable recruitment
from year to year. It is speculated that
stocks spawning in other areas of WFM01 are mixed. The bay areas are
important nursery grounds for whitefish
larvae and fry.
Lake whitefish management unit
WFM-01 is located in 1836 Treaty
waters of northern Green Bay.
Prominent features of this area include
two large bays (Big and Little bays de
Noc), numerous small embayments,
several islands (including St. Martins
Island, Poverty Island, Summer Island,
Little Summer Island, Round Island,
Snake Island, and St. Vital Island), as
well as various shoal areas (Gravelly
Island Shoals, Drisco Shoal, North
Drisco Shoal, Minneapolis Shoal,
Corona Shoal, Eleven Foot Shoal,
Peninsula Point Shoal, Big Bay de Noc
Shoal, Ripley Shoal, and shoals
associated with many of the islands
listed above). Little Bay de Noc is the
embayment delineated by statistical grid
306. Its surface area is 39,880 acres.
Shallow waters characterize the northern
end and nearshore areas, but there is a
40- to 100-ft channel that runs the length
of the bay. Rivers that flow into Little
Bay de Noc include the Whitefish,
Rapid, Tacoosh, Days, Escanaba, and
Ford. Big Bay de Noc is a larger
embayment of 93,560 acres delineated
by statistical grids 308 and 309. Big
Bay de Noc is relatively shallow with
over half the area less than 30-ft deep
and a maximum depth of 70 ft. Rivers
that empty into Big Bay de Noc include
the Big, Little, Ogontz, Sturgeon,
Fishdam, and Little Fishdam.
Trap-net yield of lake whitefish
in WFM-01 was 654 thousand lbs during
2001. There has been no commercial
gill netting in this management zone
since 1985. Total yield in 2001 was
49% lower than the short-term (19982000) average and 53% lower than the
long-term (1976-2000) average. The
2001 yield was 28% higher than in 2000
despite a 31% decrease in effort between
years. There were 2,323 trap-net lifts in
2000 and only 1,607 during 2001. Trapnet effort has declined sharply since
1999.
Commercial lake whitefish yield WFM-01
2500
2000
Trap Net
GillNet
TAC
1500
1000
500
0
Year
Waters in WFM-01 (380,652
total surface acres) offer extensive areas
where suitable habitat is available and is
likely used by spawning whitefish. The
Big Bay de Noc Shoal is documented as
93
Lake whitefish commercial trap net and gill net effort WFM-01
70
60
Lake whitefish recruitment (age-3)WFM-01
Trap Net
Gill Net
50
12
6000
10
5000
8
4000
6
3000
4
2000
40
30
20
10
2
0
0
1000
0
Year
Year
Weight-at-age for WFM-01 lake
whitefish continued to decline across all
age groups. Declining trends have been
evident through the entire data set (19762001) for some ages with highest slopes
for fish aged 5 and above. Weight-atage values (ages 3-9+) in 2001 were
down between 17 and 72% compared to
1998-2000 averages, and down 48-73%
from 1976-2000 averages.
Fishable biomass was estimated
at 5.4 million lbs in 2001 and of this
total, spawning stock biomass (3.2
million lbs) represented 60%. Both
fishable biomass and spawning stock
biomass estimates for 2001 decreased
from 2000 estimates.
Estimated lake whitefish biomass WFM-01
14000
12000
10000
Lake whitefish population mean weight at age WFM-01
Total
Spawning Stock
8000
9
6000
Age-3
Age-5
Age-7
Age-9
8
7
6
4000
2000
5
0
4
3
Year
2
1
Estimates
of
instantaneous
mortality rates were identical for 2000
and 2001. Total instantaneous mortality
rate (Z) was estimated at 0.49 y-1 in
2001, with 0.33 y-1 attributable to
instantaneous natural mortality rate (M)
and 0.16 y-1 attributable to instantaneous
fishing mortality rate (F). Instantaneous
mortality
rates
were
considered
excessively high prior to 2000.
0
Year
Estimated recruitment (numbers
of age-3 fish) increased in 2001
compared to 2000.
The 2001
recruitment estimate of 2,208,000 lake
whitefish was 45% greater than average
recruitment estimated between 1976 and
1992, but was 50% lower than the
average for years of highest recruitment,
1993-1998.
94
Instantaneous mortality rates for lake whitefish WFM-01
1.4
Natural
Trap Net
Gill Net
Sea Lamprey
1.2
1
0.8
0.6
0.4
0.2
0
Year
The projected 2003 yield limit
for WFM-01 is 1.018 million lbs. This
represents a 45% increase from the 2002
yield limit of 703 thousand lbs. The
increase was influenced by low harvest
in 2001 relative to the yield limit (654
thousand lbs vs. 796 thousand pounds),
continued low estimated mortality rates,
and an increase in estimated recruitment.
Factors that held the yield limit down
included decreases in weight-at-age and
decreased fishable biomass. Fishing
effort documented for 2001 could
increase 1.7-fold in 2003 based on
projection model outputs.
95
Summary Status WFM-01 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.20 lb
4y
1.56 lb
5y
0.573 lb
(SE 0.001)
0.24 lb
(SE 0.01)
0.138 lb
(SE 0.000)
0.425
(SE 0.016)
0.259 lb
(SE 0.006)
-1
Natural Mortality (M)
0.445 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
8
8
-1
Average gill net F, ages 4+
0. y
(SE 0.)
Average trap net F, ages 4+
0.307 y
(SE 0.022)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.752 y
(SE 0.022)
Recruitment (age-3)
(1992-2001 average)
3,543,800 fish
(SE 342,950)
Biomass (age 3+)
(1992-2001 average)
9,794,100 lb
(SE 516,450)
Spawning biomass
(1992-2001 average)
3,177,500 lb
(SE 167,930)
MSC recommended yield limit for 2003
Actual yield limit for 2003
96
1,018,000 lb
1,018,000 lb
WFM-02 (Manistique)
Prepared by Mark P. Ebener
The increase in fishery yield was
partly a function of increased fishing
effort.
Large-mesh gill-net effort
increased from 1.0 million ft in 1986 to
6.1 million ft in 1999 then declined to
0.9 million ft in 2001. The associated
gill-net yield increased from 68,000 lb in
1986 to 282,000 lb in 1999, then
declined to 41,000 lb in 2001. Gill-net
effort explained only 54% of the
variation in gill-net yield from WFM-02
and the relationship appeared to be
linear. Trap-net effort increased from 56
lifts in 1986 to 957 lifts in 1991,
declined to 412 lifts in 1996, then
increased to 1,116 lifts in 2000. Trapnet fishery yield increased from 18,000
lb in 1986 to 225,000 lb in 1991, then
ranged from 146,000 to 276,000 lb
during 1992-2001.
Trap-net effort
explained only 61% of the variation in
trap-net yield from WFM-02 and the
relationship appeared to be asymptotic
since yield did not increase after 500
lifts. Fishery effort in 2001 was made
up of 739 trap-net lifts and 0.9 million ft
of gill net.
WFM-02 is located in the
northwest portion of Lake Michigan.
There are 387,000 surface acres of water
< 240 ft deep in the unit. The only
known spawning population of whitefish
in WFM-02 is located in Portage Bay,
but this population is not as abundant as
other stocks in Lake Michigan. Many of
the whitefish that inhabit WFM-02 move
into the unit from adjacent units and
Wisconsin waters.
WFM-02 has been an exclusive
CORA commercial fishing zone since
1985. One trap-net operation and 2-3
large gill-net boats regularly fish WFM02. Little to no small-boat gill-net effort
takes place in WFM-02.
Besides
whitefish, the large-boat gill-net fishery
routinely targets bloater in the offshore
waters.
The commercial fishery yield
from WFM-02 was 302,000 lb during
1986-2001. The peak harvest from
WFM-02 was 559,000 lb in 1999 and the
lowest yield was 86,000 lb in 1986. The
average yield from the trap-net fishery
was 159,600 and average yield from the
gill-net fishery was 142,700 lb during
1986-2001. The commercial fishery
yield was 202,600 lb in 2001 of which
161,400 lb came from the trap-net
fishery and 41,200 lb came from the gillnet fishery.
Lake whitefish commercial trap net and gill net effort WFM-02
12
7
Trap Net
Gill Net
10
6
5
8
4
6
3
4
2
Commercial lake whitefish yield WFM-02
2
600
Trap Net
GillNet
500
1
0
0
TAC
1986
1988
1990
1992
1994
1996
1998
2000
Year
400
Whitefish in WFM-02 are of
moderate size. The harvest by weight
was made up of 62% No. 1 whitefish,
25% mediums, and 13% jumbos during
1986-2001. Mean weight of a harvested
whitefish in the trap-net fishery ranged
300
200
100
0
1986
1988
1990
1992
1994
1996
1998
2000
2002
Year
97
biomass averaged about 850,000 lb from
1986-1993, then increased to a peak of
2.9 million lb in 1997. After 1997
fishable stock size declined and was 1.9
million lb in 2001. Spawning stock
biomass followed a similar course as
total biomass but peaked somewhat later.
Spawning stock biomass peaked at 1.9
million lb during 1997-1999, and
declined to 1.2 million lb in 2001.
from 1.9 lb in 2001 to 3.3 lb in 1986.
Mean weight of a harvested whitefish in
the gill-net fishery ranged from 1.9 lb in
2001 to 3.7 lb in 1989. Mean weight of
harvested gill-net and trap-net fish was
lower in 2001 than any other year.
Mean weight of all age classes of
whitefish > age 4 continued to decline in
2001 and was lower than in any other
year. The declines were greater for older
fish than for younger whitefish. Mean
weight of age-9 and older whitefish
declined from 6.9 lb in 1986 to 2.6 lb in
2001. Mean weight of age-5 whitefish
declined from 2.6 lb in 1986 to 1.4 lb in
2001.
Estimated lake whitefish biomass WFM-02
3500
2500
2000
1500
1000
500
Lake whitefish population mean weight at age WFM-02
9
0
Age-3
Age-5
Age-7
Age-9
8
7
6
1986
3
2
1
0
1990
1992
1994
1996
1998
1990
1992
1994
1996
1998
2000
Total annual mortality of age 4
and older whitefish increased from 1996
through 1993, then generally declined.
Total mortality increased from 0.38 y-1
in 1986 in 0.97 y-1 1993. After 1993
total annual mortality declined to 0.45 y1 in 2001. Fishing mortality was
estimated to be 0.05 y-1 for the gill-net
fishery and 0.16 y-1 for the trap-net
fishery in WFM-02 in 2001. Natural
mortality in WFM-02 was estimated to
be 0.245 y-1.
4
1988
1988
Year
5
1986
Total
Spawning Stock
3000
2000
Year
Estimated recruitment in WFM02 increased substantially through time.
Recruitment of age-3 whitefish to the
population in WFM-02 averaged
143,000 fish from 1986-1993. After
1993 recruitment of age-3 whitefish
averaged 533,000 fish in WFM-02.
Recruitment in 2001 was estimated to be
533,000 fish.
Instantaneous mortality rates for lake whitefish WFM-02
Natural
Trap Net
Gill Net
Sea Lamprey
1.0
0.9
0.8
Lake whitefish recruitment (age-3) WFM-02
0.7
0.6
1200
0.5
1000
0.4
0.3
800
0.2
600
0.1
400
0.0
1986
200
1988
1990
1992
1994
1996
1998
1990
1992
1994
Year
1996
1998
2000
While total annual mortality of
age 4 and older whitefish was less than
the target rate of 1.05 y-1, estimated
mortality of age-8 and age-9 whitefish
was greater than the target rate.
Consequently, the projection model
0
1986
1988
2000
Year
Estimated biomass of whitefish
changed in response to the increase in
recruitment in WFM-02. Fishable stock
98
estimated that fishing mortality rate
should be reduced 6% from the rates
observed during 1999-2001.
The
recommended harvest limit at this
reduced rate of fishing was estimated to
be 514,000 lb in 2003.
The
recommended harvest level in 2002 was
estimated to be 100,000 lb, but a harvest
regulating guideline of 186,000 lb was
adopted for 2002.
99
Summary Status WFM-02 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.99 lb
4y
1.81 lb
6y
1.94 lb
(SE 0.037)
0.49 lb
(SE 0.02)
0.116 lb
(SE 0.000)
0.251
(SE 0.010)
0.651 lb
(SE 0.008)
Natural Mortality (M)
0.245 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
-1
8
8
-1
Average gill net F, ages 4+
0.206 y
(SE 0.022)
Average trap net F, ages 4+
0.270 y
(SE 0.017)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.721 y
(SE 0.035)
Recruitment (age-3)
(1992-2001 average)
585,860 fish
(SE 66,829)
Biomass (age 3+)
(1992-2001 average)
2,011,000 lb
(SE 101,770)
Spawning biomass
(1992-2001 average)
1,526,300 lb
(SE 66,864)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
514,000 lb
514,000 lb
100
WFM-03 (Naubinway)
Prepared by Mark P. Ebener
WFM-03 is located in northern
Lake Michigan. The unit extends from
the Straits of Mackinaw west to Seul
Choix Point and is bounded on the south
by Beaver Island and complex of shoals
and islands that surround the island.
Nearly the entire unit is shallow water
<90 ft deep. There are 483,000 surface
acres of water <240 ft deep in WFM-03.
WFM-03 contains several very
large
spawning
aggregations
of
whitefish. The entire northern shoreline
is part of the Niagara Escarpment thus
much of the whitefish spawning occurs
here. Large spawning aggregations are
associated with the area between
Epoufette and Naubinway, Michigan,
and in the Straits of Mackinaw along the
upper and lower Peninsulas
WFM-03 has been an exclusive
commercial fishing zone for the CORA
fishery since 1985. For that matter,
WFM-03 has been an important
commercial fishing area for most of the
twentieth century. A trap-net and both
large- and small-boat gill-net fishery
operate throughout WFM-03.
The commercial fishery yield
from WFM-03 averaged 1.065 million lb
during 1986-2001. The trap-net fishery
yield averaged 516,300 lb and the gillnet fishery yield averaged 509,100 lb
during 1986-2001. Total fishery yield
peaked at 1.9 million lb in 1993 and 1.8
million lb in 1994 and declined slowly
thereafter.
The trap-net yield was
677,000 lb and the gill-net yield 165,000
in 2001.
Commercial lake whitefish yield WFM-03
2000
Trap Net
GillNet
TAC
1800
1600
1400
1200
1000
800
600
400
200
0
1986
1988
1990
1992
1994
1996
1998
2000
Year
Fishing effort in WFM-03 has
been highly variable. Gill-net fishing
effort increased from 2.9 million ft in
1986 to 16.7 million ft in 1992 then
declined to only 1.7 million ft in 2001.
Trap-net effort varied between 565 and
2,139 lifts during 1986 to 2001 without
any significant trends. There was a
positive linear relationship between gillnet effort and yield where effort
explained 86% of the variation in gill-net
yield.
In contrast, the relationship
between trap-net effort and yield was not
linear and effort explained only 38% of
the variation in trap-net yield. Trap-net
yield appeared to be asymptotic after
about 1,400 lifts.
Lake whitefish commercial trap net and gill net effort WFM-03
25
18
Trap Net
Gill Net
16
20
14
12
15
10
8
10
6
4
5
2
0
0
1986
1988
1990
1992
1994
1996
1998
2000
Year
Whitefish in WFM-03 are of
small size. During 1985-2001 No. 1
whitefish made up 85%, mediums 12%,
and jumbos only 3% of the harvest from
WFM-03. Mean weight of a harvested
whitefish ranged from 2.0 to 3.6 lb in the
gill-net fishery and 2.0 to 2.7 lb in the
101
total biomass averaged 8.8 million lb
during 1991-2001.
Spawning-stock
biomass was more stable than total
biomass varying less than two-fold from
4.5 to 8.6 million lb during 1986-2001.
Spawning stock biomass exceeded total
biomass during 1986-1990 before the
dramatic declines in growth reduced the
proportion of mature females at ages 35.
trap-net fishery during 1986-2001.
Mean weight of a harvested whitefish in
2001 was 2.3 lb in the gill-net fishery
and 2.5 lb in the trap-net fishery.
Growth of whitefish in WFM-03
continued to decline in 2001. Mean
weight of age-2, age-3, age-7, age-8, and
age-9+ whitefish were all lower in 2001
than any other year during 1986-2001.
Mean weight of age-4-6 whitefish
increased slightly from 2000 to 2001,
but mean weight of these age-classes in
2001 was still lower than most other
years.
Estimated lake whitefish biomass WFM-03
12000
Total
Spawning Stock
10000
8000
6000
Lake whitefish population mean weight at age WFM-03
4000
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Age-3
Age-5
Age-7
Age-9
2000
0
1986
1988
1990
1992
1994
1996
1998
2000
Year
1986
1988
1990
1992
1994
1996
1998
Changing gill-net fishing effort
was primarily responsible for the
changes in total annual mortality of
whitefish in WFM-03. Total mortality
of age-4 and older whitefish increased
from 0.50 y-1 in 1986 to 0.91 y-1 in 1993,
then declined to 0.51 y-1 in 2001. Gillnet fishing mortality increased from 0.08
y-1 to 0.38 y-1 then declined to 0.04 y-1 in
2001. Trap-net fishing mortality was
fairly stable ranging from 0.6 to 0.21 y-1
during 1986-2001 and averaged 0.13 y-1.
Natural mortality was estimated to be
0.336 y-1 in WFM-03.
2000
Year
Recruitment of age-3 whitefish
was fairly consistent and high in WFM03. Recruitment increased from roughly
600,000 whitefish in 1986-1988 to an
average of 2.0 million fish during 19891993, and increased further to 2.9
million fish during 1994-2001.
Lake whitefish recruitment (age-3) WFM-03
3500
3000
2500
Instantaneous mortality rates for lake whitefish WFM-03
2000
1.00
1500
Natural
Trap Net
Gill Net
Sea Lamprey
0.90
1000
0.80
500
0.70
0.60
0
0.50
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
0.40
Year
0.30
0.20
0.10
Biomass of age-3 and older
whitefish has been fairly stable through
time in WFM-03 compared to other units
in the 1836-ceded waters. Total biomass
of whitefish in WFM-03 varied less than
three-fold from 3.9 to 10.8 million lb
during 1986-2001. During 1991-2001
0.00
1986
1988
1990
1992
1994
1996
1998
2000
Year
Total annual mortality on fully
vulnerable age-classes was less than the
target rate during 1999-2001. Further,
the spawning potential reduction at
102
current mortality rates and at the target
mortality rate were greater than 0.20.
Consequently, the projection model
estimated that fishing mortality rate
could be increased 1.92 times above the
levels experienced during 1999-2001.
The recommended yield limit at the
increased rate of fishing was estimated
to be 1,462,000 lb for 2003. The 2002
recommended yield limit was 1,313,000
lb.
103
Summary Status WFM-03 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.52 lb
3y
1.77 lb
6y
1.103 lb
(SE 0.002)
0.6 lb
(SE 0.02)
0.115 lb
(SE 0.000)
0.547
(SE 0.014)
0.341 lb
(SE 0.009)
Natural Mortality (M)
0.336 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
-1
8
8
-1
Average gill net F, ages 4+
0.067 y
(SE 0.005)
Average trap net F, ages 4+
0.141 y
(SE 0.009)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.543 y
(SE 0.013)
Recruitment (age-3)
(1992-2001 average)
2,630,800 fish
(SE 150,700)
Biomass (age 3+)
(1992-2001 average)
8,864,300 lb
(SE 346,060)
Spawning biomass
(1992-2001 average)
7,043,700 lb
(SE 262,540)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
1,462,000 lb
1,462,000 lb
104
WFM-04 (Beaver Island)
Prepared by Mark P. Ebener
880,000 lb in 1993. The average yield
of whitefish was 586,000 lb during
1981-2001. The trap-net fishery yield
ranged from 0 lb during 1986-1988 to
542,000 lb in 1981 from WFM-04, while
the gill-net yield ranged from 48,000 lb
in 2001 to 731,000 lb in 1993. The trapnet yield from WFM-04 was 217,000 lb
in 2001.
WFM-04 is located in central
northern Lake Michigan and contains a
very diverse range of habitat. There are
seven islands located in the unit mainly
along the northern edge of the unit and
associated with a large, shallow, rocky
reef complex that extends about 15 miles
west from Waugoshance Point. The
northern reef complex is shallow ranging
from 5 to 30 ft deep. To the south of this
large reef complex is located many
smaller submerged reefs located on the
east and west sides of Beaver Island.
These latter reefs are surrounded by deep
water.
WFM-04 contains 577,000
surface acres of water <240 ft deep.
There are at least several
reproductively isolated stocks of
whitefish that inhabit WFM-04, and
most, if not all, of these are associated
with the large northern reef complex.
One stock spawns in Sturgeon Bay along
the northeast side of the unit, while
another stock is found at Hog Island.
WFM-04 has been an exclusive
commercial fishing zone for the CORA
fishery since 1985. Much of the area is
designated as a lake trout refuge where
retention of lake trout by recreational or
commercial fisheries is prohibited. The
eastern portion of WFM-04 along the
Lower Peninsula of Michigan is a
favorite fishing area for CORA smallboat fisheries. The offshore waters of
WFM-04 are fished exclusively by
large-boat gill-net and trap-net fisheries.
Only trap-net fisheries targeting
whitefish operate within the refuge.
The commercial fishery yield of
whitefish from WFM-04 ranged from a
low of 265,000 lb in 2001 to a peak of
Commercial lake whitefish yield WFM-04
1000
Trap Net
GillNet
TAC
900
800
700
600
500
400
300
200
100
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
Year
Fishing effort in WFM-04 has
varied widely through the years. Trapnet effort peaked at 1,642 lifts in 1981
then declined to zero during 1986-1988.
Thereafter, trap-net effort increased
slowly and peaked at 715 lifts in 2001.
Gill-net effort increased from 4.8 million
ft in 1981 to 10.9 million ft in 1995 then
declined to a low of 0.85 million ft in
2001. The decline in gill-net effort
followed as a consequence of the 2000
Consent Decree that required conversion
of gill-net fisheries to trap-net fisheries.
105
Recruitment of age-3 whitefish to
the population in WFM-04 was
remarkably constant unlike in all other
Lake Michigan management units. An
average of 564,000 age-3 whitefish
recruited to the population of WFM-04
during 1981-2001. Annual recruitment
varied only from 234,000 to 861,000 fish
during
1981-2001.
Whitefish
recruitment was estimated to be 586,000
fish in 2001.
Lake whitefish commercial trap net and gill net effort WFM-04
18
12
Trap Net
Gill Net
16
10
14
8
12
10
6
8
4
6
4
2
2
0
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Whitefish in WFM-04 are of
moderate size. Whitefish of No. 1 size
made up 60%, mediums 24%, and
jumbos 15% of the commercial fishery
yield from WFM-04 during 1985-2001.
Annual mean weight of a harvested
whitefish in the trap-net fishery ranged
from 2.0 to 3.2 lb during 1981-2001.
The mean weight of trap-net harvested
whitefish was 2.0 lb in 2001. Annual
mean weight of a harvested whitefish in
the gill-net fishery ranged from 2.6 to
3.5 lb during 1981-2001. The mean
weight of a gill-net harvested whitefish
was 2.8 lb in 2001.
Growth of whitefish in WFM-04
has not declined to the same extent as
whitefish in other Lake Michigan units.
Age-9 and older whitefish experienced
the most significant decline in mean
weight as they declined from 9.1 lb in
1981 to 2.6 lb in 2001. The decline in
growth of younger age-classes occurred
primarily after 1994. Mean weight of
age 3-5 whitefish did increase slightly
from 2000 to 2001.
Lake whitefish recruitment (age-3) WFM-04
1000
900
800
700
600
500
400
300
200
100
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Biomass of age-3 and older
whitefish was also fairly stable in WFM04 as a consequence of the consistent
recruitment. Total biomass ranged from
1.9 million lb in 1984 to 3.8 million lb in
1996. Spawning stock biomass ranged
from 1.9 million lb in 1984 to 3.8
million lb in 1995. Spawning stock
biomass and total biomass were nearly
equal in all years prior to 1996,
thereafter, spawning biomass was
always less than total biomass.
Estimated lake whitefish biomass WFM-04
4000
3500
Total
Spawning Stock
3000
Lake whitefish population mean weight at age WFM-04
2500
10.0
9.0
8.0
7.0
2000
Age-3
Age-5
Age-7
Age-9
1500
1000
500
6.0
0
5.0
4.0
3.0
Year
2.0
Mortality of age-4 and older
whitefish in WFM-04 generally declined
through time. Total annual mortality
1.0
0.0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
106
declined from 0.95 y-1 in 1981 to 0.54 y-1
in 1989, increased to 0.72 y-1 in 1993,
then declined to 0.38 y-1 in 2001. The
gill-net fishery accounted for nearly all
the fishing mortality of whitefish in
WFM-04 during 1986-1999 when gillnet mortality ranged from 0.15 y-1 to
0.41 y-1. Trap-net mortality ranged from
0.0 y-1 to 0.54 y-1 during 1981-2001.
Gill-net mortality was 0.02 y-1 in 2001,
whereas trap-net mortality was 0.13 y-1
in 2001.
Natural mortality was
estimated to be 0.231 y-1 in WFM-04.
Instantaneous mortality rates for lake whitefish WFM-04
1.0
Natural
Trap Net
Gill Net
Sea Lamprey
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Year
Total annual mortality of all ageclasses of whitefish was less than the
target rate of 1.05 y-1 during 1999-2001.
The current spawning potential reduction
in 2001 was 0.47 and the spawning
potential reduction at the target mortality
rate was estimated to be 0.40. The
projection model estimated that fishing
mortality rate could be increased 1.33
times from the fishing level experienced
during 1999-2001. The recommended
harvest limit at this increased level of
fishing was estimated to be 540,000 lb.
The recommended yield limit was
639,000 lb in 2002.
107
Summary Status WFM-04 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.71 lb
3y
1.62 lb
4y
2.587 lb
(SE 0.004)
1.19 lb
(SE 0.03)
0.354 lb
(SE 0.000)
0.458
(SE 0.013)
0.698 lb
(SE 0.012)
Natural Mortality (M)
0.231 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
-1
8
8
-1
Average gill net F, ages 4+
0.114 y
(SE 0.008)
Average trap net F, ages 4+
0.146 y
(SE 0.011)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.492 y
(SE 0.017)
Recruitment (age-3)
(1992-2001 average)
614,330 fish
(SE 40,026)
Biomass (age 3+)
(1992-2001 average)
3,013,200 lb
(SE 108,910)
Spawning biomass
(1992-2001 average)
2,688,600 lb
(SE 90,474)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
108
540,000 lb
540,000 lb
WFM-05 (Grand Traverse Bay)
Prepared by Mark P. Ebener and Erik J. Olsen
Much of the tribal fishing activity that
occurred prior to and immediately after
re-affirmation of treaty-reserved fishing
rights took place in Grand Traverse Bay.
CORA small-boat fishermen relied on
Grand Traverse Bay as an important
fishing ground because the Bay contains
deep water located close to shore, and
because it offers small-boat fishermen
protection from wind and waves. WFM05 has been an exclusive tribal
commercial fishing zone since 1985 and
WFM-05 waters of Grand Traverse Bay
have been an exclusive commercial
fishing area for the Grand Traverse Band
since 1985.
Initial tribal fishing activities in
WFM-05 were focused on an exploited
population of whitefish. Commercial
fishing by state-licensed fisheries had
been prohibited in WFM-05 for several
decades before tribal small-boat
fishermen began fishing the area in the
late 1970s. Initial yields in 1978 and
1979 were in excess of 400,000 lb and
jumbo (>4 lb) whitefish made up more
than 90% of the yield.
Harvests
increased to >500,000 lb in 1983 and
1984, but by then jumbo whitefish made
up only 30% of the yield.
Commercial yields of lake
whitefish were substantially less during
the decade of the 1990s than during the
1980s. The commercial yield averaged
384,000 lb from 1980-1989 and 208,000
lb during 1990-1999. The fishery has
declined through the late 1990s with the
lowest recorded yield coming in 2000
yield at only 53,000 lb. The large-mesh
gill-net yield has exceeded the trap-net
Management unit
WFM-05
encompasses the area from Little
Traverse Bay through Grand Traverse
Bay and offshore waters of Lake
Michigan north and west of the Leelanau
Peninsula. Much of WFM-05 contains
water >240 ft. deep including the both
the east and west arms of Grand
Traverse Bay. The deepest parts of
WFM-05 exceed 600 ft., both in the
offshore waters west of the Leelanau
Peninsula, as well as within the east arm
of Grand Traverse Bay. Several small
shallow reef areas are located in the
offshore waters and there is an extensive
shallow water area associated with the
Fox Islands. Seventeen statistical grids
make up WFM-05, but only 488,000
surface acres, or 46% of the water in
these grids, is less <240 ft. deep. Much
of the offshore waters of WFM-05 are
part of the northern Lake Michigan lake
trout refuge.
There are at least four
reproductively isolated stocks of lake
whitefish
that
inhabit
WFM-05.
Discrete spawning stocks of whitefish
are found in both the east and west arms
of Grand Traverse Bay, and in the outer
Bay associated with Northport Bay
based on mark-recapture studied
conducted by Michigan State University
researchers. There probably is another
spawning stock of whitefish associated
with the Fox Islands based on size and
age structure of fish caught at the
islands. Another, but smaller, spawning
stock is likely found in Little Traverse
Bay.
WFM-05 has been an important
tribal fishing area since the 1970s.
109
except for 1994 and 1995, during 19812000. Gill-net fishermen in WFM-05
claim the decline in catchability has been
caused in part because the gill nets
commonly become coated with an algal
slime that makes the net highly visible to
whitefish. Whatever the cause, it is
obvious that something is reducing catch
rates of whitefish to the large-mesh gillnet fishery in the unit.
yield in every year except the period
from 1994 to 1999.
Commercial lake whitefish yield WFM-05
600
Trap Net
GillNet
TAC
500
400
300
200
100
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
Whitefish CPUE WFM-05
Year
160
Pounds per 1000 ft.
140
4
3
3
2
1
0
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
100
0
Whitefish from WFM-05 are
currently of small to moderate size. The
proportion of the yield made up of the
three size classes of whitefish were 71%
No1 (<3 lb), 22% mediums (3-4 lb), and
7% jumbos (>4 lbs) during 2000-2001.
This compares with 65% No1, 22%
mediums, and 13% jumbos from 19801989 and 65% No1, 20% mediums, and
15% jumbos from 1990-1999.
As illustrated earlier, size
structure of whitefish in the yield from
WFM-05 has changed over time, as the
proportion of jumbos declined and the
proportion of No1 whitefish increased.
Annual mean weight of whitefish
sampled from trap-net harvests ranged
from 2.0 to 3.6 lb since 1979 and
averaged 3.2 lb during the last three
years (1999-2001). Annual mean weight
of whitefish in the gill-net harvest
ranged from 2.4 to 3.5 lb since 1979 and
averaged 2.9 lb during the last three
years (1999-2001).
Growth of whitefish from WFM05 has remained very stable through the
2
1
200
Year
5
4
300
60
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
6
5
400
80
0
7
6
100
20
7
Trap Net
Gill Net
500
40
Commercial Fishing Effort WFM-05
8
120
600
Gill Net
Trap net
Pounds per Lift
Large-mesh gill-net effort in
WFM-05 declined almost every year
since 1984, whereas trap-net effort has
varied, but with a downward trend since
1996. Gill-net effort declined from 6.4
million ft. in 1983 to a low of only 1.7
million ft. in 2001. Trap-net effort has
varied annually between 200 and 800
lifts during 1982-2001. Since 1991,
trap-net effort has averaged 344 lifts per
year, peaking out at 790 lifts in 1996,
with a low of 66 in 2000.
9
700
180
2001
Year
The decline in yield of whitefish
in WFM-05 has mirrored the decline in
lake whitefish recruitment within this
management unit. In addition, there is
an apparent decline in catchability of
whitefish to the large-mesh gill-net
fishery. CPUE of whitefish in the largemesh gill-net fishery declined from 153
lb per 1,000 ft. of gill net in 1979 to17 lb
per 1000 ft. of gill net in 1999. On the
other hand, CPUE of whitefish in the
trap-net fishery has been remarkably
stable between 150 and 300 lb per lift,
110
years, unlike the pattern of declining
growth seen in other areas of Lakes
Michigan
and
Huron,
including
substantial declines in areas adjacent to
this management unit. Mean weight of
ages 3-9 whitefish showed no trends
through time in WFM-05 from 1981 to
2001, although some age classes did
weigh slightly less in 2001 than in 1981.
Estimated Recruitment Age-3 Whitefish WFM-05
800
700
600
500
400
300
200
100
0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Population Mean Weight at Age WFM-05
6.0
Year Class
Biomass of whitefish estimated
with the stock assessment model
declined in response to declines in
recruitment.
Annual biomass of
whitefish >age 3 calculated at the
beginning of each year were peaked at
the beginning of the 1981-2001
timeframe with 3.3 million lb. This
steadily declined to 1.5 million lb in
1989, rebounded to 2.0 million lb in
1994 and has declined to only 979,000 lb
in 2001. Spawning stock biomass also
followed the same trend peaking at 3.3
million lb in 1981 and declining to
973,000 lb in 2001.
Age-3
Age-5
5.0
Age-7
Age-9
4.0
3.0
2.0
1.0
0.0
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Recruitment of age-3 whitefish to
the population in WFM-05 was highly
variable and has declined lately based on
estimates from the stock assessment
model. The number of age-3 whitefish
entering the population has declined
significantly over time. The 1978-1983
year classes were estimated to range
from 340,000 to 591,000 fish. From
1981-1989, the average was still
relatively high at 421,000 fish per year.
More recently, the average has dropped.
From 1992-2001 only 238,230 age-3 fish
were estimated to be entering the fishery
each year. It is difficult to assess whether
the decline in recruitment is real, or an
artifact of changing catchability to the
gill-net fishery.
Estimated Biomass WFM-05
4000
Total
Spawning Stock
3500
3000
2500
2000
1500
1000
500
0
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
Year
Fishing mortality (F) in WFM-05
has been split about equally between the
gill- and trap-net fisheries in recent
years.
Average fishing-induced
mortality on whitefish >age 4 averaged
0.10 for the large-mesh gill-net fishery
and 0.05 for the trap-net fishery during
1999-2001. Gill net-induced fishing
mortality ranged from 0.31 in 1984 to
0.08 in 1999, while trap-net-induced
fishing mortality ranged from 0.21 in
111
1996 to 0.01 in 1981. The gill-and trapnet mortality level has declined from a
combined rate of .48 in 1996 to .20 in
2001.
Total annual mortality on the
fishable stock in WFM-05 during 19992001 was substantially less than the
target rate of 65%.
Total annual
mortality was estimated to be 48%
during 1999-2001 and the spawning
potential reduction value was 0.59.
Consequently, the projection model
estimated that fishing mortality could be
increased 4.35 times in WFM-05 in 2003
from the average value during 19992001. The projected yield associated
with this level of fishing was 345,000 lb,
and was accepted as the recommended
maximum yield in 2003.
112
Summary Status WFM-05 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
1.90 lb
4y
2.54 lb
5y
2.562 lb
(SE 0.)
1.51 lb
(SE 0.05)
0.314 lb
(SE 0.000)
0.588
(SE 0.021)
0.609 lb
(SE 0.030)
-1
0.335 y
Natural Mortality (M)
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
10
10
-1
Average gill net F, ages 4+
0.10 y
(SE 0.01)
Average trap net F, ages 4+
0.047 y
(SE 0.004)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.482 y
(SE 0.013)
Recruitment (age-3)
(1992-2001 average)
238,260 fish
(SE 12,886)
Biomass (age 3+)
(1992-2001 average)
1,394,900 lb
(SE 73,202)
Spawning biomass
(1992-2001 average)
1,158,300 lb
(SE 66,127)
MSC recommended yield limit for 2003
Actual yield limit for 2003 (HRG)
113
345,000 lb
345,000 lb
WFM-06 (Leland - Frankfort)
Prepared by Philip J. Schneeberger
in 2001, trap-net yield was 68.4
thousand lbs (94%) and gill-net yield
was 4.5 thousand lbs (6%). Proportions
of yield by gear type have varied
considerably from year to year with an
average split of 77% from trap nets and
23% from gill nets between 1985 and
2001.
Lake whitefish management unit
WFM-06 is located in 1836 Treaty
waters west of the Leelanau Peninsula
from about Cathead Point south to
Arcadia. Surface area for this unit is
945,156 acres (including part or all of
grids 709-714, 808-814, 908-912, and
1008-1011). These waters of Lake
Michigan include Good Harbor Bay,
Sleeping Bear Bay, and Platte Bay. Two
large islands, North Manitou and South
Manitou, are contained in this
management zone, as are three large
shoal areas including North Manitou
Shoal, Pyramid Point Shoal, and
Sleeping Bear Shoal.
Major rivers
flowing into WFM-06 include the Platte,
and the Betsie.
Betsie Lake is a
drowned river mouth formed where the
Betsie River flows into Lake Michigan.
Except for areas near shore or around the
islands, most of the waters in WFM-06
are deep (>200 ft). Bays, islands, and
shoal areas offer the best habitat for lake
whitefish spawning in this management
area. Most trap-net effort and harvest is
reported from grids 812-814 and 912
(areas associated with the abovementioned bays).
Commercial lake whitefish yield WFM-06
250
200
Trap Net
GillNet
TAC
150
100
50
0
Year
Trap-net effort increased 41%
from 2000 to 2001 while gill-net effort
decreased 88%. The 2001 trap-net effort
(332 lifts) was 24% above the 19852000 average, but gill-net effort
(246,000 ft) was 49% lower in 2001 than
for the 1985-2000 average.
Lake whitefish commercial trap net and gill net effort WFM-06
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
WFM-06 was reserved for statelicensed commercial trap-net-fishing
operations from 1985 through 1999,
except that tribal gill netting was
allowed in grid 714. Beginning in 2000,
WFM-06 became a shared zone in a
truer sense of the term, and waters were
opened to both state and tribal fishers.
3
Trap Net
Gill Net
2.5
2
1.5
1
0.5
0
Year
Yield for 2001 was 73 thousand
lbs in WFM-06, down from 123
thousand lbs in 2000, but 51% higher
than the 1985-2000 average. Of the total
Lake whitefish weight-at-age in
2001 continued to be level with values
from 1998 through 2000 for ages under
114
7. Declines in weight-at-age have been
documented for fish aged 7 to 12+ over
the last six to eight years. Weight-atage values in 2001 for fish aged 3-12+
were 22-55% lower than 1985-2000
averages.
Estimated lake whitefish biomass WFM-06
800
Total
Spawning Stock
700
600
500
400
300
200
Lake whitefish population mean weight at age WFM-06
100
8
0
Age-3
Age-5
Age-7
Age-9
7
6
5
Year
Total instantaneous mortality rate
(Z) in 2001 was 0.50 y-1, showing a
decrease in the rate for the second year
in a row. Based on current estimates, the
2001 rate for Z is 22% higher that the
average for 1985-2000. Instantaneous
fishing mortality rates (F) have varied
considerably for trap nets and gill nets
throughout the time series. During 2001,
F was almost entirely attributable to the
trap-net fishery. Estimates for F were
0.22 y-1 for trap nets and 0.01 y-1 for gill
nets.
The 2001 estimate for
instantaneous natural mortality rate was
0.26 y-1, still the largest source of lake
whitefish mortality in WFM-06.
4
3
2
1
0
Year
Recruitment, based on estimated
numbers of age-3 fish, was lower in
2001 than any year since 1993.
Estimates of recruitment were highest
during 1994-98 and lowest for the time
series during 1987-88.
Lake whitefish recruitment (age-3)WFM-06
180
160
140
120
Instantaneous mortality rates for lake whitefish WFM-06
100
0.7
Natural
Trap Net
Gill Net
Sea Lamprey
80
0.6
60
0.5
40
20
0.4
0
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
0.3
Year
0.2
0.1
Estimates of fishable biomass
and spawning stock biomass have been
stable relative to other management
zones, and have roughly paralleled each
other from 1985 through 2001. Values
estimated for 2001 were 454 thousand
lbs for fishable biomass and 415
thousand lbs for spawning stock
biomass. The ratio of spawning stock
biomass to fishable biomass was 0.92 in
2001. The ratio averaged 0.97 from
1985 to 2000.
0
1
2
3
4
5
6
7
8
9 10
Year
11
12
13
14
15
16
17
The 2003 yield limit is 221,000
lb - virtually the same as the limit
calculated for 2002. The projection
model shows that the 2001 level of effort
may increase 3.7-fold for gill nets and
1.6-fold for trap nets as one way to reach
the 2003 yield limit.
115
Summary Status WFM-06 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.46 lb
3y
1.19 lb
4y
3.929 lb
(SE 0.007)
1.43 lb
(SE 0.09)
0.369 lb
(SE 0.000)
0.363
(SE 0.022)
0.863 lb
(SE 0.023)
-1
Natural Mortality (M)
0.264 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
8
8
-1
Average gill net F, ages 4+
0.113 y
(SE 0.01)
Average trap net F, ages 4+
0.149 y
(SE 0.016)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
-1
Average ages 4+,1999-2001
0.526 y
(SE 0.026)
Recruitment (age-3)
(1992-2001 average)
85,573 fish
(SE 6,704)
Biomass (age 3+)
(1992-2001 average)
558,830 lb
(SE 46,787)
Spawning biomass
(1992-2001 average)
507,660 lb
(SE 44,942)
MSC recommended yield limit for 2003
Actual yield limit for 2003
116
221,000 lb
221,000 lb
WFM-07 (Ludington)
Prepared by Archie W. Martell Jr.
within this unit. The larger minimum
length limit within this unit has
biological implications such as an
increase in the average number of
spawning opportunities per female. In
2003 LRBOI adopted the CORA 17-inch
minimum size limit on lake whitefish for
this unit. This decision was based upon
review of the length distribution of lake
whitefish within the unit and the percent
of their relative abundance, from graded
mesh surveys, at <19-inch and <17-inch
minimum size limits.
This review
indicated that under the <19-inch
minimum size limit that only 44.0% of
the population was available for harvest,
and 83.4% was available under the <17inch minimum size limit. The average
size, in length, of a lake whitefish in this
unit from graded-mesh gill-net surveys
was below the minimum size limit of 19inches as indicated in the table below for
2000-2002.
Lake whitefish management unit
WFM-07 is located within the 1836
Treaty Ceded Waters of eastern central
Lake Michigan from Arcadia in the
north to just south of Stony Lake, and
west to the state line bisecting the
middle of the lake. This lake whitefish
management unit includes part or all of
grids 1107-1111, 1207-1211, 1306-1310,
1406-1410, 1506-1510 and 1606-1609.
The surface area for this unit is
1,286,940 acres (2,011 square miles) of
which 274,943 acres (430 square miles)
have bottom depths of 240 feet or less
with maximum depths up to 900 feet.
There are no islands, or bays and apart
from the shoreline, inflows from the
Manistee, Little Manistee, Big Sable,
Pere Marquette, and Pentwater Rivers,
and drowned river mouths at Manistee
Lake, Pere Marquette Lake, and
Pentwater Lake this area has few other
obvious distinguishing features relevant
to lake whitefish biology.
There has been no modeling of
lake whitefish stocks in WFM-07 by the
Modeling Sub-Committee of the
Technical Fisheries Committee due to a
lack of current long-term commercial
catch information. At this time no
harvest limits have been set for this unit.
Pursuant to the 2000 Consent Decree,
the tribes have three years of allowable
commercial fishing without harvest
limits in this unit. During the three-year
period, the tribes are limited to an effort
restriction of two trap-net operations
with twelve nets each.
Since 2000, WFM-07 has been a
Tribal commercial fishing zone for lake
whitefish, part of the Little River Zone
with tribal fishing regulated under
permitting control of the Little River
Band of Ottawa Indians (LRBOI).
There has not been any tribal or
significant state commercial fishing
effort for lake whitefish in this unit from
1985 through 2000.
The current
regulations prohibit the use of largemesh gill nets and only allow for use of
large-mesh trap nets for commercial lake
whitefish exploitation. In 2001 LRBOI
enacted a 19-inch minimum size limit,
rather than 17-inches under the CORA
regulations, on lake whitefish harvest
At the conclusion of the 2003
fishing season, Tribal fishers will have
conducted three years of commercial
fishing activity for lake whitefish within
117
levels represented by the 1978-1989
average. Historical graded-mesh gill-net
CPUE of 4.3/1,000 feet for lake
whitefish from spring surveys is
represented by the average for 19781989. Between 1999 and 2002, gradedmesh gill-net surveys CPUE for lake
whitefish in spring assessments ranged
from 1.4, 4.5, 6.1, and 6.5/1,000 feet
respectively.
this unit. Pursuant to the 2000 Consent
Decree, and the Tribal Management
Plan, a Harvest Regulation Guideline
(HRG) for lake whitefish will have to be
developed for this unit for the 2004 and
future fishing seasons.
Commercial fishing harvest of
lake whitefish within WFM-07 for 19812002 peaked at 124,735 pounds in 1984
represented mostly by large-mesh gillnet effort of 684,700 feet. All largemesh gill-net effort for commercial
fishing was eliminated in this unit by
1986. Current Tribal commercial fishing
activities for lake whitefish began in
2001. These activities were limited and
effort was distributed only in October
and November with a total harvest of
6,361 pounds from 5 trap-net lifts. In
2002 Tribal commercial harvest was
23,165 pounds with 29 trap-net lifts.
WFM-07 CPUE from Spring LWAP Assessments
7
6
5
4
3
2
1
0
78-89 Avg.
120
Gill Net
Trap Net
80
60
40
20
2001
1999
1997
1995
1993
1991
1989
1987
1985
1983
1981
0
Year
WFM-07 Commercial Fishing Effort
50
Gill Net
Trap Net
700
600
500
40
30
400
20
300
200
10
100
2001
1999
1997
1995
1993
1991
1989
1987
1985
1983
0
1981
0
2001
2002
Recent (2000-2002) mean weight
and mean length of lake whitefish
sampled in spring graded-mesh gill-net
surveys has declined as compared to the
average from 1978-1989. The mean
weight and mean length of commercially
harvested lake whitefish have declined
when comparing 1983 to 2001-2002.
The mean age of lake whitefish in spring
graded-mesh gill-net surveys has
increased for 2000-2002 as compared to
the 1978-1989 average. Also, the mean
age of lake whitefish from commercial
harvests has increased for 2001-2002 as
compared to 1983. Mean weight at age
for younger age groups is similar from
graded-mesh gill-net surveys in 2001
and 2002 compared to the 1978-1989
average. However, the disparity in mean
weight at age between recent surveys
(2001 and 2002) and the historic average
is much greater for older age groups,
with the historic average being much
larger.
WFM-07 Commercial Fishery Yield
800
2000
Year
140
100
1999
Current relative abundance of
lake whitefish in WFM-07 appears to be
increasing when compared to historical
118
Year
Gear
1978-1989 Avg.
1983
2000
2001
2001
2002
2002
GMGN
CF
GMGN
CF
GMGN
GMGN
CF
Mean TL (inch) Mean Wt (Lb)
23.34
23.32
18.61
19.89
18.96
18.44
19.34
6,000
1978-1989 Avg.
2001 LWAP
2002 LWAP
4,000
3,000
2,000
1,000
0
2
3
4
5
6
7
8
4.8
7.3
6.1
10.9
9.9
8.9
9.7
historical information are showing signs
of decreased weight at age and an
increase in mean stock age.
WFM-07 Mean Weight at Age
5,000
6.84
5.54
2.22
2.76
2.37
2.33
2.69
Mean Age
9 10 11 12 13 14 15 16
Age
The instantaneous total annual
mortality rates for WFM-07 lake white
fish were determined from catch curve
analysis. The instantaneous total annual
mortality rate (Z) for 1978-1989 spring
graded-mesh gill-net survey averaged
0.20 y-1 for ages 3 through 15. The
instantaneous total annual mortality rate
(Z) for 2001 and 2002 spring gradedmesh gill-net survey averaged 0.13 y-1
for ages 6 through 16, and 0.03 y-1 for
ages 5 through 13 respectively.
The lake whitefish stocks within
WFM-07 are relatively unexploited as
compared to other management zones in
northern Lake Michigan. There are
indications that the abundance of lake
whitefish is increasing within this
management unit. The current spring
graded-mesh gill-net surveys and the
commercial harvest as compared to
119
WFM-08 (Muskegon)
Prepared by Philip J. Schneeberger
during 2001 was 29% higher than the
1985-2000 average, whereas 2001 effort
represented a 26% decrease from the
average for 1985-2000.
Management unit WFM-08 is the
Lake Michigan whitefish zone from
about Montague south past Port Sheldon.
WFM-08 has a surface area of 1,506,880
acres in Michigan grids 1706-1710,
1806-1810, 1906-1911, and 2006-2011.
Apart from the shoreline, inflows from
the White, Muskegon, and Grand rivers,
and drowned river mouths at White
Lake, Muskegon Lake, Mona Lake, and
Pigeon Lake, this area has few other
distinguishing features relevant to lake
whitefish biology. Depth gradients west
from shore are relatively gradual, but
most of the waters in WFM-08 are 200ft deep or deeper. More than three
quarters of the trap-net effort and over
80% of the trap-net harvest is reported
from grid 1810.
Commercial lake whitefish yield WFM-08
3500
3000
2500
Trap Net
GillNet
TAC
2000
1500
1000
500
0
Year
Lake whitefish commercial trap net and gill net effort WFM-08
10
9
8
7
6
5
4
3
2
1
0
Although
commercial
exploitation and monitoring have
occurred for many years, little is known
about reproductive biology of the WFM08 lake whitefish stock. Fish in this area
are near the southern end of the
distribution for lake whitefish.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Trap Net
Gill Net
Year
Weight-at-age data have trended
downward from 1985 through 2001.
Considering a shorter time frame
comparison, 2001 weight-at-age values
were 11 to 46% less than averages for
1998-2000 for ages 4-8. However, fish
9-years old and older were generally
heavier than for corresponding ages
averaged from 1998 to 2000.
Two
state-licensed
trap-net
fishers operate in WFM-08 where
minimum length for whitefish in
commercial catches was 19 inches TL
through 1999, then changed to 17 inches
TL in 2000. Other management zones
have had a 17-inch minimum size limit
throughout the time series. Through
2001 there has been no gill net harvest of
lake whitefish in WFM-08.
Lake whitefish yield from WFM08 in 2001 was 274 thousand pounds.
This yield was a 67% increase over the
previous year despite a 10% decrease in
effort between 2000 and 2001. Yield
120
Estimated lake whitefish biomass WFM-08
6000
Lake whitefish population mean weight at age WFM-08
9
8
7
6
Total
Spawning Stock
5000
Age-3
Age-5
Age-7
Age-9
4000
3000
5
2000
4
1000
3
2
0
1
0
Year
Year
Mortality rates have been
relatively stable throughout the time
series. Instantaneous total mortality rate
(Z) was estimated at 0.40 y-1 during
2001. Components of the total rate
consisted of 0.12 y-1 for instantaneous
trap-net-fishing mortality (F) and 0.28 y1
for instantaneous natural mortality (M).
The ratio of F to Z averaged 0.34 from
1985 through 2001.
Recruitment, based on the
estimated number of age-3 fish, was
622,000 in 2001.
Estimates of
recruitment were considerably higher
(average 1,384) during 1998-2000, but
the estimate for 2001 was more than
double the 1985-1997 average of
310,000 age-3 fish.
Lake whitefish recruitment (age-3)WFM-08
Instantaneous mortality rates for lake whitefish WFM-08
2500
0.6
2000
0.5
Natural
Trap Net
Gill Net
Sea Lamprey
0.4
1500
0.3
1000
0.2
500
0.1
0
0
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
1
Year
Estimates of fishable biomass
and spawning stock biomass continued
increasing trends that have persisted
since the early 1990s. Fishable biomass
was estimated at 5.6 million lbs and
spawning stock biomass was 5 million
lbs in 2001. The ratio of spawning stock
biomass to fishable biomass was 0.90 in
2001, slightly lower than the 1985-2000
average ratio of 0.95.
2
3
4
5
6
7
8
9 10
Year
11
12
13
14
15
16
17
The 2003 yield limit for WFM08 was 1.852 million lbs, calculated
using the projection model. This yield is
very close to the limit calculated for
2002. Projection model output indicated
that 2001 trap-net effort could be
increased by a factor of 4.9 to target the
2003 yield limit.
121
Summary Status WFM-08 Whitefish
Female maturity
Size at first spawning
Age at First Spawning
Size at 50% maturity
Age at 50% maturity
Spawning biomass per recruit
Base SSBR
Current SSBR
SSBR at target mortality
Spawning potential reduction
At target mortality
Average yield per recruit
0.60 lb
3y
2.35 lb
4y
3.477 lb
(SE 0.007)
2.05 lb
(SE 0.11)
0.375 lb
(SE 0.000)
0.589
(SE 0.032)
0.538 lb
(SE 0.035)
Natural Mortality (M)
0.280 y
Fishing mortality rate 1999-2001
Fully selected age to Gill Nets
Fully selected age to trap nets
-1
10
-1
Average gill net F, ages 4+
0. y
(SE 0.)
Average trap net F, ages 4+
0.116 y
(SE 0.016)
Sea lamprey mortality (ML)
(average ages 4+,1999-2001)
-1
N/A
Total mortality (Z)
Average ages 4+,1999-2001
-1
0.396 y
(SE 0.016)
Recruitment (age-3)
(1992-2001 average)
774,940 fish
(SE 127,130)
Biomass (age 3+)
(1992-2001 average)
3,477,900 lb
(SE 413,680)
Spawning biomass
(1992-2001 average)
3,119,200 lb
(SE 362,790)
MSC recommended yield limit for 2003
Actual yield limit for 2003
122
1,852,000 lb
1,852,000 lb
N
Lake Superior
W
E
WFS-00
WFS-02
S
WFS-05
WFS-01
WFS-03
WFS-06
WFS-07
WFS-04
WFS-08
WFH-03
WFM-02 WFM-03
WFM-01
WFM-04
WFM-00
WFM-05
WFH-01 WFH-02
WFH-04
WFH-05
WFM-06
WFH-06
Lake Huron
WFM-07
WFH-07
WFH-08
Lake Michigan
WFM-08
WFM-09
30
Appendix 1. Lake whitefish management units.
123
0
30
60 Miles
N
Lake Superior
W
MI-1
E
S
MI-3
MI-2
MI-4
MI-5
MI-6
MI-7
MI-8
MH-1
MM-1
MM-2 MM-3
MH-2
MM-4
MM-5
MH-3
MM-6
Lake Huron
MH-4
MH-5
Lake Michigan
MH-6
MM-7
MM-8
20 0 20 40 60 80 Miles
Appendix 2. Lake trout management units.
124